Just about all of the Mustang suppliers carry them (Ponderosa, NPD, Mustang Unlimited, Virginia Mustang.....the list goes on). They come both bolt-on and weld-on. From what I gather here, most people prefer the weld-on. That will be the route I take when the time comes.
summit, jegs, any mustang book, run you between 75-150 probably. you can get either bolt on of weld, id recommend weld on b/c bolt ons will stretch the holes and become lose and cause probs... if you do weld make sure the car is sitting as close to "normal" stance as it can be so you dont weld them on when the frame is already twisted b/c it will stay that way.... dont know the other stuff you asked..
I got mine from Mustangs Plus. Most of the Mustang parts places sell one kind or another. There seems to be a few different kinds. They can bolt in or weld in or both. The front part was welded and the rear bolted initially on mine. I had the rears welded later on.
I got mine from CGS Chassis! I was very pleased with their service and quality. I don't know if they sell on the web or via phone, because I got mine from ehay. They currently have a listing, see item # 2424962255. You can buy it now for $55.00, but I elected to bid and got them for $40.
I got them back in Feb. and they had an ice storm. They kept in contact with me and let me know the minute they shipped. I was very pleased!
I bought the CGS chassis too, very unimpressed with the design and fitment, would have taken a 5 lb hammer to bend them up for an acceptable fit.. paid $55 for $10 worth of square tubing that was pretty poorly deisgned IMO. Tossed them on a shelf and payed the price for the TCP.. another case of you get what you pay for.