Yeah they can be pricey. Bikes don't need much though, a basic Miller TIG welder will do. You'll need AC and high-frequency for best results on alloy. Welding thin-wall tubing is completely different than anything else. Due to their delicate nature, attention to little details makes a big difference. Such as flushing the tubing with gas as you weld. Even pre-filling the tubing beforehand makes a difference as well.
Kinda hard to get double-butted 7005 alloy in just the right lengths though. I ended up trimming them externally on a lathe.