MF is the same whether bought from the developer or resale, though I don't know what that number is. Obviously the best way to find a deal on eBay is to shop on eBay. You can email some of the sellers, they don't always post everything they have, but then you might be opening yourself to paying the 'Buy it Now' price. Another way might be to check the completed auctions, and offer a few bucks to those sellers that got no bids on units you want. A caution here: units that get no bids often have something wrong with them. Too small, wrong season, parking lot view, high AI fees could be examples. The TUG Marketplace as another place to shop for resales.
Be open to other resorts. Mini systems often allow low cost exchanges within the system, even though they are weak traders in the large exchanges. Pueblo Bonito comes to mind as well as UVC. Personally, I'd steer clear of Vida (Grupo Mayan). Nice resorts, but predatory sales practices and they have prejudicial practices against resale buyers and owners of their 'lesser' properties. They always press owners to upgrade.
You would do well to rent- at least for your next vacation or two. Hang around TUG Learn the ins and outs of TS ownership. The last few years, while the economy has improved, so have TS defaults, so owners have been faced with rapidly increasing MFs to pay what the deadbeats don't. Hence, rentals are low in price, while MFs are high. Consequently you can often rent for lower cost than the owner is paying in MF.