I've picked up quite a few of the ponies like you're selling; HTF but in poor to fair condition.
Personally, I wouldn't have put an offer in on them. The ones I bought all had a listed price and I was just lucky to get in there first. If I were in your position, I'd get price checks in the corral and then list the ponies on here for those prices, assuming that you were happy with them.
I don't know how well trades would work; generally I think people want to trade several common-er ponies for one rare-er pony, which wouldn't work well with your space issue.
As for selling off the more common ponies, small lots tend to work quite well on here. I've been using this site recently to check PayPal fees and found it to be 100% accurate on my transactions:
http://paypalfeecalculator.paymentprocessing.cc/