Those horses don't really seem like "rescues" persay at least not from the descriptions you posted..
A rescue needs to take only the number of horses it can afford without having to post craigslist adds begging for hay and grain or charge an arm and a leg for a horse that is only sound for plodding around the pasture (speaking in general, not this rescue). I think it is fair of them to be looking to get back the adoption rescue fee of the horse, and some more of their expenses if they can. However they should not be looking to make profit, IMO.
Considering the prices of horses right now, I would be very picky with rescuing (Especially because of Crimsonshorse's point that you never really have true ownership of the horse, no papers generally, etc). If I am going to spend $2500 on a horse, I'll probably just buy it.
Personally, I would rescue a horse if I was looking for something to pamper and ride for fun and wouldn't spend more than a grand on one. I want the rescue to stay open if it is a legit rescue, but it's usually not the best financial decision.
...and don't even get me started on the PMU "rescues"