Aaron - Tell your friend Lou to check out http://www.maximummotorsports.com/onlinecat.html
for info on pricing. I went with a torque arm package, which included the heavy-duty torque arm, panhard bar, and height adjustable rear lower control arms for around $1270. The normal torque arm is $200 cheaper, but can only take 425lb-ft (at the flywheel), and I'm probably over that. Anyway, add in some H&R rear springs for another $139.
As for exhaust clearance, I think the Flowmaster pipes will be a problem around the panhard bar bracket. The bracket is designed to clear the stock exhaust routing, which Dynomax follows pretty closely, but apparently Flowmaster is a bit different. I had Flowmaster 3-chambers with Dynomax tailpipes on the car for years, so you could always do that. The Dynomax tailpipes are pretty inexpensive, much cheaper than the Flowmaster ones.
As for the subframe connectors, MM says the KB ones aren't strong enough to take the loads imparted by the torque arm. They recently began selling some add-on pieces that weld to the KB SFCs to make them taller (hence stronger in bending), or you can chop out the KB ones and get full-length MM SFCs. That's what I did, and I kinda wish I hadn't - if the KB SFCs are welded in there well, it's a huge PITA to get them out.
Last but not least, can you do it yourself? I dunno. Give the guys at MM a call - they're extremely friendly and helpful, and will tell you everything you need to know.
Feel free to email me with more questions (email@example.com) so we don't bore the Subaru crowd with too much Mustang babble.