once it's gone I'm going to budget £300 a month for flying which at my club buys just over 3 hours in a 172/28 or just under 4 in a 152
My word what club are you residing at (very interested, I may consider a block booking)? The cheapest club rates here in the North England are £130ish for C152 and between £140-60ish for PA28 C172 per wet hour.
Obviously there are private run clubs which offer a more cost effective option, but don't forget to factor in the monthly running costs and in some cases the initial cost of share equity.