Whats the deal with my 273 engine on eBay?

Everything on ebay goes that way. Depends on when the buyers arrive.
What brings only 20 this week might bring 60 next week.

Think that happened to me in reverse - bought a 273/235 from a 66 Formula S 4 speed Barracuda on ebay for a measley $150.00 - only 2 bidders. Had to drive like 200 miles to pick it up but that was no big deal. Other than the Commando valve covers and chrome air cleaner, it was a complete motor. After hot tanking the bore only needed a hone so the original high compression pistons could be used. The rods and mains were all standard so everything worked out great money-wise. It will be a perfect replacement for the 273-2 in my 65 Barracuda.