Hit your local classifieds and see what is going for sale.
I've bought a couple of fantastic bikes second hand, including a Pegeout 753 pro with Ultegra for £225 and a Mercian Superstrider with Campy for £200.
You've had your bike long enough to know what you like and what you don't. Also take your cycling shorts and a 5mm allen key with you when you go to have a look at a bike so you can take it for a test spin.

Also worth checking your local bike club web site as they often list bikes for sale.

And remember to haggle, so go look at £400 bike and then explain you only have £325 and its cash.

Have fun looking.