Sadly the only cheap way is with home made compost. Some local authorities will sell you compost, but often only in large quantities and if you provide your own transport.

And local authority compost may turn out to contain bits of plastic and the like... No idea if there are lots of riding stables in Essex but if there are you may be able to get well rotted horse manure, which will have straw in it too, fairly cheaply.

I can only agree with both Boggy and MG. As a cheapskate I always try to do it myself. Making compost is not quick but it is easy and if you want it for your garden you have the main resource to hand - your garden.

Sorry but I forgot to add that horse manure has, as MG says, to be well rotted. Round here I can often get fresh horse pooh free, well rotted costs. If you can get fresh free it must be stored for a year or two before using. Premature use, because of nitrites from the urine in the pooh, can kill plants.

And watch out for Aminopyralid weedkiller contamination of animal manures. Look it up to see how to check for its presence.
If you have not got the space for a compost heap or bin, then try the compost trench idea. Dig a spade and a half deep trench across the part of the garden you wish to compost. Fill the trench up with all manner of bio-degradable material. When the trench is full, cover it over with soil from the next trench and begin again. I did this in our first garden with good results. The nice thing is the stuff does not need to be well broken down, the soil does it for you.

I have 3 compost bins, I shred paper, use kitchen waste, cardboard, old plants, leaves and so on but I need to turn it sometimes, amazing the worms that appear. Looks we don't live far from each other, I sometimes go to a Garden Centre near you 'Morley Nurseries' expect you know of it :o) I have seen free manure on the way to Canewdon also on Freecycle web site. :o)

Even well rotted lawn mowings help soil texture. (Takes about two or even three years to rot though)If you can get hold of fallen leaves in autumn and shred with them with your mower you can lay them down as a winter mulch and dig what's left of them in in the spring, though the worms take down quite a lot. . If you are worried about nitrogen depletion caused by rotting down you can always add some high N fertiliser in March. I have greatly improved some miserable clay soil by doing just this over several years. Ive used fresh mowings as a mulch round bushes in poor soil with no noticeable ill effects and the soil does get better.
Another advantage of winter mulch is that the blackbirds and thrushes love digging in it for their dinner!

If you use the trenching idea you can put in seaweed (if you are near the coast!) it is a good conditioner and holds moisture. I use it on top of my asparagus bed too - it keeps most of the weeds down and takes ages to rot. (if using on other crops - rinse salt off it first)
If you have room buy/borrow/steal some comfrey roots and split them up (v small bits will root)plant them through a membrane or hessian-backed carpet (if possible - to deter weeds) once established you will have an eternal supply of rich mulching material. We planted up a steep bank above our stream (awkward for anything else) and we cut it 3-4 times a year, to begin with we laid it complete on beds around perennials and chopped the rest with a machete (hard work!) but it fed the plants brilliantly and kept weeds down. A couple of years ago we invested (i think £260) in a (viking ge250) shredder - after borrowing our neighbours to test! - it worked wonderfully. Now we can get through all the comfrey in an afternoon and cover 3 or 4 big beds. Then we started shredding our miscanthus grass (it grew too high anyway!) that made a good mulch too. We shred hedge trimmings and 'tougher' prunings onto perennial areas, and keep the comfrey/ miscanthus for the veg. We even shred Gunnera stalks in autumn!
One tip tho' - long-sleeved shirt is essential - lots of shredded plants can cause irritation.
Other cheap mulches - get cardboard boxes from shops (esp huge ones - fridge boxes etc) cut to the shape of your beds, hose down with water to get them to 'stick', they will last a season. Use hessian-backed carpets (be careful there are no plastic fibres - they don't break down!) you can usually get them from your local tip or skip company.-, or even new stuff from carpet stores - they always throw loads away!
If you want a long-lasting mulch that will gross your family out - collect the hair trimmings from hair-dressers/barbers! It lasts for years, covers the ground well and stops many weeds - and comes in a lovely range of colours!
If you see a house being re-thatched (it happens in Devon!) stop and ask if you can have the old thatch, great for growing spuds under.
Being skint is an excellent way of training the mind to see possibilities in the strangest of places! If a substance is natural, it generally will break down in the presence of water/air/light, and generally it will be useful as a mulch. So keep your eyes - and mind - open!

Forgot to say - grass cuttings are fine - as long as its earlier in the season before it has set seed, and as long as the layer is only 3-4 inches thick, it will still last for a couple of months. I always use it around seedlings - carrots/parsnips etc, as it is easy to lay down.

All very good ideas, however I would warn against planting Comfrey unless you can get hold of the non-seeding variety (Bocking something or other). We have it growing wild in the hedgerow near us and it seeds into our garden and it is a b...... to get out. Also both my wife and I are very sensitive to the leaves. Touch them without gloves and we are rashed!
Also forgot to mention Green manures. Sow in Autumn and dig in in Spring.
Of course much of this this advice is for an empty garden. Mulching with organic mater is the only way if your garden is already well planted up.

Yes comfrey can be a pain spreading, but the bees love it, they really do.

It is Bocking 14 Boggy. I will be thinning my roots of this in early spring (March) and if anybody wants a couple of roots then PM me with your address. It spreads but is certainly not as invasive as the viable seeding varieties so will take a couple of years to establish. Makes excellent fertiliser, better than tomato food.

Not for us thank you. As I said we dare not touch it without gloves so it is removed as soon as we see it. Have enough trouble with back ache and arthritis without having my hands turned to very itchy red blobs.

Yes, allergies can be pretty bad, and I understand common with comfrey. We're lucky and aren't allergic to it but Jacqui comes out in a rash if she touches Echium pininana so we've had to stop growing that.

I fetched 200 compost bags of Horse Manure from a farm where the daughter keeps 2 cart horses as pets.
Marvellous stuff. Its a pain to fill the bags, but free.