It does work, if it's on a springer then you won't notice the difference as the mech is firing next to your ear, but further down range it makes a big difference, even if you can't here it. And if you use a Weihrauch silencer, all the better.
Second hand s200s are about £300 without a scope. so with a budget of £200 with a decent scope, don't think that'll do.
Co2 is rubbish, Pre-charged are amazing, and springers are amazing. Vermin shooting really needs a good dome headed pellet, Anything else isn't up to the job. Pointed pellets are good on Pigeons and that's about it.