[Dale]

With that kind of budget, you are probably looking at a spring sporter and I would recommend the Weihrauch HW97K, as I use it myself. The only complaint I have about it is the weight. You will also need to budget for a scope and you can get a cheaper end one for around £50 or so. You may be better off looking at the second hand market as you may get a decent scope as well for your budget but beware, as with all things second hand, there are some dodgy guns and kit out there.

Tuning means just that, a bit like tuning a car and basically, it means working on the insides of a spring rifle in particular, to maximise its performance and make it more user friendly.