I agree with the 2nd hand Alecto suggestion, but disagree that spring pistols are rubbish - they just take a bit more work!

A few other ideas:
New Baikal IZH-53M (well under your budget, shoots well, long sight radius)
2nd hand HW45 (classic, well made, good trigger, won't lose money if you sell it on)
New Crosman 1377 (multi-pump pneumatic, very customisable)
2nd hand BSA Scorpion (classic, very powerful)


Avoid like the plague:
BSA 240 magnum
Newer Webleys (Alecto notwithstanding)
HW70
SMK crap