At my local Petsmart, a 55 tank is $120 and a stand is at least $180. I'd say as long as the tank isn't 10 years old and the stand doesn't look like a monkey built it, it's a pretty good deal.
As to the UGF, it won't work with sand. I assume it comes with a powerhead. If it does, scrap the UGF and keep the powerhead and use it for water movement. Buy a good hang off filter like an Emperor 400 or Aquaclear 110 and you'll be all set. These pop up frequently on the buy & sell forum here for around $20-$25.
You can even sell the UGF to recoup some of your money for the hang off. I know a lot of people don't like them, but I've used one with some success with African Cichlids (with gravel). If you change your mind about the sand and go with gravel, set up the powerhead for reverse flow so it pushes water up through the gravel in addition to the hang off.