If you have any other welder at home you may want to consider a High Frequency TIG box that you add onto an arc welder as you sure learn a lot for using one. I started with a Airco High Frequency TIG box and then moved to Miller HF251 with foot pedal. I will say the learning curve was quite steep with these machines but it was the cheapest route as I picked up each TIG HF box for around $300 off of Craigslist with torch usually. The other nice thing is that you are never short on power as I have found with entry level TIG machine.
The other route was to pick up an old Miller Econo Twin, not the Econo Tig, to learn as you can not hurt those machines which can be important when learning. Probably the same money to give you an idea what you would want in your next machine.
The only thing I will suggest is if you want a new High Frequency TIG, get something in the 200 amp range as that should take care of most of your needs especially with thicker aluminum.