Welcome to the forum mate, just depends what exactly you mean by a fortune. I know paintball markers are pretty expensive as well but not sure what kind of budget you'll be looking at. Also are there are particular guns you like the look of? I wanna point out gas isn't the best thing to go for if you are just starting - usually because of people's inexperience and not having the commitment to maintain em all the time, but also cos they are so expensive.
From what I know WE are quite a 'go-to' brand for GBBRs as they're probably the most inexpensive, and they do M4s / SCARs / L85A2 etc. PTS just came out with a Magpul Masada for £360 IIRC. Honestly you're looking at least 250 that's basically the cheapest you're gonna get a gas rifle.
You might wanna consider a Tippmann M4 as they can be run on HPA like a paintball gun, potentially you could use some of your existing pball gear for that rather than spending £50+ on a new one. They're 400 quid...but it's cheap compared to SMP / P* setups which are drop in replacements for the standard gearbox in an AEG yet cost about as much as the Tippmann alone just for the fusion engine unit.
In all I'd say start off with a JG G36 / G&G Combat Machine M4 / CYMA AK (the top three recommended beginner electric guns) to get a feel for it and so you're able to play with your own gun. Then you could move up to something better or upgrade it. Alternatively, go and hire for a few games, you're not gonna have spent a load on your own gun only to find out you don't enjoy it.
Spring are worthless (only for backyard plinking) unless you mean sniper rifles, but even they aren't worth the money (you need to spend a lot on upgrades to make them really good, otherwise performance is as same as an AEG but you're limited by mag capacity and rate of fire etc)
Hope this helps