Maybe you've already shopped their site, but if you don't need it to say "MarkBass" on it and want good value for your hard-earned, check these guys out:
Custom Amp Covers - We make the covers that no one else does
Bought a cover for my Hartke from them early this year. Very happy with the materials, construction, fit, price and turnaround time.
I think if you try to go any lower than the price you mention, you're getting into nickel-and-dime territory. Good luck!