+1 on the TIG and depending on what you are welding you don't need to spend a ton of cash.
I was at your exact point six months ago. I've been doing a bunch of projects with intercooler and intake tubing so I bought a spool gun being cheap since I've been bleeding money this year finishing out the shop. I was tacking the tubing and having a buddy I know with a TIG finish it out but that got old fast. The spool gun is heavy and sloppy and welds like crap. Fortunately for me all of the tubing i was doing was being ground down and painted- Heaven forbid I wanted to polish it out.
I picked up a Miller Diversion 165 from my brother a few months back- he bought it, used it twice, and it sat in his garage for two years. I think he paid about $1500 and I bought it from him for $1000 with a bunch of aluminum rod. Its a 220V welder so it will do anything I need. There was a learning curve from MIG to TIG but since it sounds like you know your way around a MIG you should do fine. I've had it about two months and although I'm not laying dimes yet but I'm getting there. Best advise I can give you is buy a foot pedal and practice on thin wall tubing or expensive radiators- it teaches you control!
There was no way I was going to let myself burn through a $1400 radiator while welding on brackets!!