The first decision will be power source ... spring/gas ram or pcp. To state the obvious (maybe) springers are self contained, pcp need an air source, pump or air bottle which adds to the cost.

Although I have not seen them myself there seems to be quite a few new springers on the market that get pretty good reviews; think price range around £200-£250. Similarly pcps at around £500 without bottle etc. Some come with a scope/bag, otherwise add around £80 for a basic scope, sometimes with mounts. Moving upmarket a bit with springers brings you into Air Arms, Weihrauch territory with good ranges of break barrels from Weihrauch and underlevers from both AA and Weihrauch. Diana may figure at some shops as well.
If you can, it will be best if you can visit a shop to see a selection of rifles in order to handle / shoulder them, maybe even test fire. Hopefully the shop may have a number of s/h ones as well. This is better than selecting a model blind. I note you are in B'ham. I am sure a search will reveal several shops within a reasonable distance. A search on Guntrader should reveal who has what.
Good luck, and welcome aboard.

Cheers, Phil