Whether you buy a new tank or reseal the one you have depends on a few things.
1. How much the cost of a tank means to you, and how valuable your time is. For some people $40 is a lot of money, for some people, the several hours to reseal a tank is a long time.
2. How skilled you are with DIY type projects.
These instructions look pretty good:
Aquamaniacs :: View article - How to Reseal Your Glass Aquarium - by Jake DeTommaso
You can transfer your HOB filter to a new tank and add fish. However, you may have a mini-cycle, so keep a close eye on parameters and make sure you stock very lightly with hardy fish, just to be safe.