Hmm... Just to make sure I'm clear on this idea, the used stuff for sale is for the benefit of the seller. Right? Kind of a single place for a aquarium focused yard/garage sale?
If it was for the benefit the club, I've got stuff I'd be willing to bring. But it would likely end with things like old heaters and such. But if it's going in MY pocket I'd bring some $400 pumps, old Neptune controllers and other awesome stuff.