I think you have to ask yourself why it is you want to learn to tune. If you just want to get an understanding of it then just get yourself a book. Anything by Greg Banish is a good read. If you want to make money from it and learn it to the point of it being a business then look into the couple schools out there, like the Tuning School.
Here’s where I’m going to sound a little hypocritical, if you plan on tuning your own car then just save your money and pay a competent tuner. While I feel very confident in tuning gen 3 GM stuff and tweaking most cars, I would not consider myself a tuner. I started down the learning to tune just because my stubborn ass didn’t want to pay someone to do it. After years of learning, many books, and learning many lessons to hard way by breaking shit, I wish I’d have just paid to have it done correctly and left it alone. At this point I am glad I understand it as being a technician it really helps me to understand how everything works, but it was a really expensive and frustrating road.
In short, is $500 worth it? No. What I suggest is reading a book. Do you think you’ll get a good return on this investment?