I'm going to go in an entirely different direction:
Coilovers: $1000
4x100 conversion: $200 (in tooling and studs)
6UL 17x8 + nuts: $1000
Used Cobb AP: $400
Pearce Motorsports 2-Point Lower Brace: $100
Check out the Fast Ford's article on light weight wheels on an earlier model FiST; the performance increase of lighter wheels is one of the best price/performance modification you can make. The Cobb AP is a great deal, even if you just start out with the OTS tunes for now. Coilovers improve ride significantly and the brace really helps turn in.
Alternatively you could stay 4x108 and use the TD 1.2's as they did in the Fast Fords article and spend the $200 on a tune, instead (and get FFS). Having said that, I love my 6ULs.
Keep in mind that I'm an autocrosser, have a race car for HPDEs, have never seen a strip, and don't street race, so you might be looking for something completely different from your FiST.