I believe I bought 1987 Mark VII rotors when I did my swap last year. Stanger9219 and chatcher are right though, you might just want to go with the SN95 stuff. My front brakes consist of 1999-current spindles, rotors and calipers. I also used a 1986 SVO master cylinder, and summit proportioning block. As for the rears, I am using the Mark VII components, which needed modifications to work. I bought them from someone in the Mustangworks Classifieds alreaddy modded (I'll see if I can find the site with directions for modifying the brackets tomorrow). They seem bulky compared to the Sn95s. I wish I had found this site before buying the rear brakes.
http://www.discbrakesrus.com/make/ford/mustang.htm#rearendflangekit
As far as costs, I don't know if the Mark VII brakes are any cheaper than the SN95 once you purchace them from a salvage, use them for cores when you end up buying remanufactured callipers to be sure they are servicable. I spent $90 for the rear calipers and $185 in a rear 5-lug Motorsport axles/drums, because I wasn't too thrilled with the axles I got in the classifieds. In the long run, for future upgrades, SN95 would seem cheaper. .
At the very least get '87-93 11" spindles and Mark VII rotors. The '79-'86 10"ers suck! SVO or MarkVII 73mm callipers would help too. I have always had good luck with MPS and their prices are pretty reasonable, especially when they have sales.
BTW, I wish my '85 had only 19K on it.