If the cube wasn't solved when you got this problem, it could be that the two edges adjacent to it were flipped, making it look like only one edge was flipped. The 4x4 OLL parity alg would've flipped them.
I have seen people find old 1980s cubes for less then $10 at Yard sales, Thrift stores, and Flea markets. If I were to look up that same puzzle on ebay it would cost way more then $15.
Also is there a place where I can buy Fitted stickers for my Dayan Megaminx if not then How do IZO Megaminx set look on a Dayan Megaminx?