Of the pistols you have listed on one has a trigger anywhere near good enough & that is the Gamo compact, The CP1 and all its derivatives fall well short in terms of their trigger,

As for CO2 you can pick up some bargains with match grade triggers, FWB, Walther CP1, CP2 etc (not to be confused with the SMK CP1) can be purchased now for around £200, are superbly accurate and have proper match triggers, they do require bulk fill but this is actually very easy and no more equipment is required other than a cylinder, an old CO2 fire extinguisher can be used and there are plenty of posts regarding filling, If i were looking for something at the budget end I would not hesitate in buying any of these, chances are you'll use it for a while and be able to sell it at exactly what you paid for it,

Mechanical options would be any of the FWB65/80/90 series, Original/Diana Mod 6/10 great pistols, superb triggers and accurate, there are still example around at sensible money although these do often get high prices also for nice examples. Walther Lp2/3's can also be found for around £200 and can the FAS604, again all very good. Gamo Compact would also fit this category and often come up at around the £120 mark,

Another very viable option is the Drulov lov21, not a pretty pistol but very accurate, a better trigger than the SMK and a chap on here even make a palmshelf and accessories to fit which will give you far better grip and stability, do not underestimate how accurate these little ugly ducklings can be, I would consider selling mine simply as I purchased it for my son who has now upgraded, not a selling pitch as i'm more than happy to keep it but an option if you want it,