My advice is this. Do not bother to buy a cheap gun to repair. I sold a Daisy 717 minter in box for £65 a couple of months ago. If you want a gun to repair, get a high quality one that is faulty or damaged selling at a greatly reduced price. After working on it you will have an excellent usable investment.Higher quality pistols are usually have better designed solid components which are interesting to make.For instance the Drulov DU 10 sometimes crop up in non working condition at reasonable prices.
Baz