there's a few candidates...depending on budget, but these of the two i have experience of

FWB300...the SU variant offers more fit options, but the S is just as good. A recoiless springer...very capable. Watch for breach seals breaking. A good workhorse, always in demand and made for target work. The lock time is slower than a pnematic, but it teaches good discipline because of that.

FWB600 series... a single stroke pump pnematic, so faster locktime. Probably a better trigger as well than the 300 by a smidge. In it's day, a medal winner. Seals again can be a weakpoint, but there is backup from some gun shops like city air guns.

Prices vary enormously...i've seen good guns go from £ 150 all up to £ 400 for both guns privately and you can find them more expensive for mint shop offerings. If you aim for about £200-300 that might give you the option on a 600 or a mint 300 su.

garvin on here is the font of all knowledge for classic 10m gear, and wonky donkey is a top chap for the top flight stuff.

be prepared though, it's very addictive...it takes a bit of perseverance to start with for the first few sessions, but when that hook goes in, it goes in deep