Nooooooo. You can get older mountain bikes of much higher quality than the Earl for $100 easy. You don't need a new rear wheel either. If it's a cassette hub you just need spacers and a cog, if it's a freewheel hub you just need an SS freewheel. And a chain tensioner if it has vertical dropouts (which most MTBs since about 1990 have, unfortunately.)

Price wise, converting an old bike to SS is the way to go for a cheap commuter. If budget isn't a concern or you want something you can ride today, by all means get a new bike. I must say though, I think the Earl is way overpriced. Steel everything, and a plain steel frame (not even chromoly!) There are far better choices, unless you enjoy riding around on a 30+ lb tank.