you can see if the tank leaks, and if it does, you can probably seal it up with silicone? dont know if you looked at the tank before you bought it, but i would have tested it at the pet shop to see if it leaked before i gave up 30bucks. about the top you can always buy a new top from a lfs.
if it leaks, than turn it into lizard tank or turtle tank(depending on how high/low the crack is) that would be cool.
if you want a cheap tank, got to
http://www.glasscages.com , build your own stand and canopy(if you want one) and buy the other accesories if you have them. and your set. prolly run you about 500(depending on what size tank you get) hope all this helps!