Sell some old crap parts and make a big deal about it whenever anything sells, buy a new bike as parts it in a more low key way.
I tried accumulating a bike fund by doing some bike mechanics for mates, unfortunately this backfired when she got wind of a fund and decided to spend it on the family. Aparenly if I can afford to spend X in a new bike/parts I much have that much spare, so for every £1 I spend I need to spend £1 on the family.
£450 is very cheap, you must have “saved” a fortune.