6ft fencing is the only instant solution as hedges/shrubs need time to grow.
As you cannot afford fencing what about something across your garden nearer the house rather than down the boundaries? Some trellis across the garden will help with privacy and you can grow plants up it to add more.

Hmmmm!!! there's a ton of different responses to this issue are'nt there? rangeing from a 'polite word' ( not always possible or effective as we folk know ) to instant fencing or slower hedging. You mentioned a 'shared' hedge, cannot this be allowed to grow the extra height required or does the neighbour take responsibility to cut it ? This is a perennial problem for so many folk now as we are being jammed in tightly together more & more. Dont know who said it first but the phrase ' Tall hedges make good neighbours ' is so true. Hope you can resolve this one without chucking tomatoes at each other. btw: I planted privet to address this very issue.

Our neighbour with whom we are on good terms. Told us how many time we had been out last week. More than me he chirped, and I've been on holiday. We hadn't noticed he was 'on holiday' as we aint nosey. I pointed out the weather was good, and this last week was op/chemo week for GJ, who will be out of sorts for days on end afterwards. We don't speak as much over the back fence in summer when the shrubs get taller. I don't mind people looking as long as they are friendly. At least they know us oldies are still alive.

Try ventetian blinds in windows, let light in, but can't see in

light weight nets? or if its plants whynot some of the taller non invasive bamboos and other grasses.

Could you strategically place a standard shrub or obelisk with an evergreen clematis so that he can't see into your room ?
If none of the suggestions suit you could try a friendly wave next time he peers in.He may think you haven't noticed and just carries on snooping.