+1 To the MTB route. Myself, I am a big fan of the older, rigid frame mtbs. They are plentiful, cheap, and the better ones were well made. And replacement (used) wheels are also plentiful and cheap. I picked up a set of wheels a couple of days ago, complete with tubes, tires, and cassette, for $4. I figured the tubes alone covered that price. Obviously a deal, but I have seen plenty of them for $10 or less.
For that price of a new Mamba, you can buy 10 or more used rigid frame mtbs. Your choice. The last new bike I bought was 1974. Since then, everything has been used. Its not uncommon to find 10 to 20 year old bikes, that have been ridden less than 50 miles. A lot of bikes are bought for the best intentions, and then sit idle.