Could be a really cool project. Do you have more information besides the water volume? What are the dimensions? Have you seen pics? What is the condition?
Also, is the sale just for the tank itself, or does it come with stand/canopy? Just having taken on a project like this last summer, I can tell you that you are about to engage in a HUGE job. Of course, as stated by others, the price of filters, skimmer, lights, rock, sand, salt, etc. will dwarf the cost of the tank alone. Additionally, if you are going to be rehabbing a damaged/badly scratched tank and building a stand and canopy for this beast, then you are looking at probably 6-10 months of prep before this thing's ready for water.
Not trying to be negative because it sounds awesome. But I don't envy the work that goes into setting up something like this. In determining placing in your basement, I'd try to leave as much access as possible for cleaning and scraping algae. With a tank that size, scraping can be VERY difficult. Good luck and let me know if you need any advice.
