Remans have dropped off because nobody was turning in a good core anymore, or some ECU's were simple no longer usable. Many were buying A9L's to do mass air swaps on speed density 5.0's and returning the SD ECU as a core, which cannot be used. Attrition is slowly reducing the number out there. Good, functioning ECU's are selling for $300+. (Speed density ECU's sell for much less however).
The same happened to 03-04 Cobra steering racks, and 93 Cobra boosters. Guys would buy these, and return non-equivalent parts as cores. As a result, no good cores means nothing to rebuild to offer for sale. Try and find a 93 Cobra booster today. I sold a reman unit for $300 not too long ago because you can't find them now.
Really, the only option available today is ECUexchange, pay the $300+ for a used mass-air ECU, or go with an aftermarket system.
The aftermarket ECU option may not be the best for some who still need to pass emissions or smog as most setups don't come ready to control things like the EGR, air pump system, evap. Some guys can make it work though, but for the most part people installing aftermarket ECU's aren't concerned with this.