The fork will be the tough thing to get on budget if you are after a Fox 36/Lyrik class 160mm one.
Your front wheel is highly unlikely to fit a 20mm through axle too. If you are staying with QR to use yr existing wheels then CRC will have some decent forks on budget, or you could get the Sektor Coil with maxle lite they are doing for £200 and buy new wheels too.
My frame choice would probably be the Commencal Meta 55 – £400 (without shock). Budget £150-200 for a decent shock if you shop around.
Kona Dawgs look alright too (£450 with shock), but the Commie will probably ride better.