Hey Ben. The quantity of tape on eBay really goes up and down but there's usually quite a few. I started collecting old tapes 3 or 4 years ago and there's more now then then. On any given week, there's probably two times more now. I think the main reason for this is that there are more sellers who are specializing in reel to reel. It used to be that the majority of tapes were being sold by folks that sold everything or records/cd's with just a couple of tapes here and there. Since the Tape Project, the number of tapes that have resulted in bidding wars increased dramatically. The sellers took note of this and began to search out lots of tapes in the hopes that a few would bring crazy high prices. About a year ago, there was a feeding frenzy on jazz and classical tapes being bought by bidders from Europe and Asia. These guys were bidding whatever it took to get the tapes they wanted. I followed the activity of a couple of them and it wasn't unusual for each of them to spend close to $2000 a week. And this went one every week for months. Since they were bidding against each other the selling prices got totally crazy (very often selling for $75 to $200 more than the normal price). A good bit of that inflation still exists but it has gone down from where it was 6 months ago. You can imagine how elated the sellers must have been when a tape that they purchase as part of a large lot for $1 each sold for $250. And when they sometimes sold 5-10 in a week many said " forget these Barbie doll outfits, where can I get more of these tape things?". But, just like Beanie Babies, the big money buyers get what they want pretty quickly and things tend to quiet down after a while. But the sellers who were forward thinking, reinvested some of their new found wealth into buying more stock. For the most part they didn't know why this tape sold for 100 times the amount of the others they had for sale and unless they happened to be music collectors themselves, they didn't have time to figure it out either. So they bought everything they could find with storage space being the only limiting factor.
Fast forward to the present. There's more demand but for the most part, the deep pockets have come and gone except for the collectors that are always looking (when I say collectors, I mean collectors of a particular band or era). It's useless to bid against these guys because they will get what they want. Someone that just wants to listen to a tape hasn't got a prayer bidding against them but the collectors are an important part of the food chain. They keep interest up with the sellers. They're happy to sell 30 tapes with $4 profit as long as every 2 weeks or so they sell one with $200 profit. That keeps the tapes flowing and out of the landfill (which, you can be sure, is where they'd been going until this latest surge of interest started).