Well speaking from a place of experience, your best bet for your first suit would be buying previously worn, or at least fabricated to wear complete pieces. Kits can be messy, time consuming, and require you to buy lots of extra stuff and if I know anything about making something, it's always nice to be able to learn with the first thing you have. Kits can run as high as $650 even. Over half of what you'd pay for a really nice previously owned set. The beauty of previously owned is that you know someone wore it at least once, and that it's at least that wearable. Ok so the AT-AT driver has a few unique pieces, and some more common pieces, You will want a tie pilot helmet (unpainted and pulled from white ABS plastic) a tie pilot chest box (same deal as the helmet) special AT-AT driver gloves, special boots and leg warmers, piloting harness, tie pilot chest armor (white), Snow trooper shoulder armor, and greeblies for your helmet, back piece, wrist mounted comlink, and a gray flight suit.
Sounds like a lot, but when you think of troopers and how every inch of them is covered in plastic armor it really isn't. and will be much more comfortable. You'll also want some decals for your helmet.
Say the word and i'll post a WTB listing on the forums.