My advice would be to choose a bike carefully; too many seem to chuck time and money at a particular bike only to find that when it's done, they don't much like it.
A C15 takes a similar amount of time and money to an A10, but you may find a 250 slogger ain't really lighting your candles.
My other bits of advice are a) if you buy a bike in bits then as a rule of thumb price the value of the engine, forks, frame etc then add it all up and offer that as a max price, and b) if you're feeling cold, or pi**ed off, or hung-over and don't really want to be knocking old iron around, then don't, as you'll only rush or spoil something. It's supposed to be enjoyable, after all.
Basically old, big, sporty and complete is generally good and sought-after, but commuter, tiddler, obscure, or basic rolling chassis, isn't.