300 USD for the set. Don't take ebay sales figures as valid information on how much your items are worth.
scandoubler is difficult to find at all now.
cards were selling retail for $179 but are no longer available....so that changes the picture.
ebay sales are high, to some degree, because of the currency conversion and are being driven by buyers in the UK/Japan,etc. who are getting items at a discount.
Asking prices are usually on the high side if someone's taking offers...and I set things less than recent sale prices.
(I think selling together at $300 would have seen them go in seconds if only for the scandoubler and the buyer may have ended up reselling the graphics card for nearly 2/3s of that and gotten a deal on the scandoubler.)
For the record, I've used/tested 3 scan doublers...the Deb 2000, the one Amiga made and this one...they all worked but this one is superior! If you want a scandoubler and one that will work with your graphics card this is the one to have.