Hey Tom, welcome to the forum, im not the best person to advise you on gas rifles, as all of my gas stuff pistols & shotguns.
I will say ive seen G36 series guns on here, usually with a few mags, for between £160-£250, mostly WE I think ?, not sure how good they are.
Next question, how much airsoft experience do you have & what does your current armoury consist of ?, because if you're just starting out & in your words "i want something to insert gas & bb's in & just go, with no problems, with something that goes with my glock", then a gbb isn't that straightforward, can be temperamental in hot, or cold extremes, mags are heavier & lower capacity, & you'll often find yourself outgunned by literally almost every aeg.
Not trying g to put you off, just give the best advice for your situation ?