You do need to be in the right place at the right time with older rifles, collectors have pushed up prices but often target shooters are more realistic although the gun may not be cosmetically perfect, you want to be carefull to ensure they are sound, best are sound untouched, or rebuilt by a known and respected expert, tampering with power is rife as is the garden shed expert who is not as sharp as they believe.
I have just bought an ex club good mechanically but not cosmetic conditition FWB 300SU on behalf of another club for £180, a member recently bought a FWB 600 (a 601 I think) for £300 so they are out there if you are patient.
There is a good Walther LGR on Stirton for £250, which is good value, I'm surprised its still there.

Best of Luck and Good shooting.