Tig has much higher investment and take some practice to do it right. If you don't do it frequent enough, every time you weld, you need to practice your skill and you better have a large tank since it will go fast. Cheaper just send it out and have professional do it for you. That is what preventing me from getting a Tig.
It depends on your definition of "much higher investment". There are some budget priced tig welders on the market today that probably do a fair job on lighter weight steel and aluminum. These are a bit more expensive than the big box hardware store 110v mig welders but not what i would class as "much higher".
I consider myself a hobby welder. I build stuff in steel like some folks work in wood.
While I do not have experience with the budget priced tig welders, my 110v mig welder does a good job within its limitations. The limitations can be frustrating though. I am sure the budget tig welders have similar limitations and frustrations, particularly when it comes to delicate work.
But, what you get when spending more money is a more capable and flexible welder, both tig and mig.
I have what I would call a medium priced transformer tig welder and I rarely fire up the mig welder or do oxy-acetylene any more.
Roger, if you weld only once in a blue moon, your skills will atrophy regardless of the mode. But, the tendency with tig welding is to do more delicate welding making the loss of skill more critical.
I figure you do not get really good at welding until you have laid down 1000 pounds of filler rod.
At least for the foreseeable future, I would still take my gun smithing welding projects to a professional.