My 10g started off as a WalMart kit for $50. The heater sucked, then died, and the included filter was decent (at best). The hood is decent as well, but again nother special. For the same $50, I could have spent the money better by getting the tank itself locally and everything else online. Friend of mine bought a 29g and a 55g Wal Mart kit, BOTH the heaters died and he lost some fish. That makes 3 dead heaters out of 3 possible from these tanks. If you add in Christmasfish and oscarbreeder, that is FIVE DEAD HEATERS OUT OF FIVE. I have no idea how they can sell that, I would think they would put a bit more work into the heaters since it is critical to keeping the fish alive.
I would not factor the heater into the purchase of the Wal Mart kit. Assume that you will have to buy another one from the start. Also, if you plan to have a hefty bioload, the included filter is not that great either, so you might not want to include that in the price either. You can get filters and heaters really cheap online luckily...
Shop around locally for a tank, and hood combo. Sometimes a pet store will throw in some freebies too, then you can buy a heater and filter online. Many times you can get a much better setup for a little bit more money. If stuff is expensive locally, go for the Wal Mart setup, just do not use the heater under any circumstance.