Tecmo Bowl is beloved by fans of the NES and is regarded as the best sports game on the system. It would only make sense that a prototype copy of the game would demand some crazy prices.
A seller who goes by sonics78 has put up a NES prototype of Tecmo Bowl up for sale on eBay. The seller has been selling on eBay for years and has a 99.5% positive feedback rating and is a known member of NintendoAge. Sonics78 also recently sold prototype copies of Tecmo Baseball and Ninja Gaiden.
The seller is currently asking $1,750 for the prototype.