There are many used tanks around these days too-people downsizing out of trucks and people upgrading to a new tank for their new truck! ANyhow-I'd check out ebay and craigslist if you're looking to save some bucks...(new lines and a solenoid are my one fix to suggest! and maybe a bottle of AL polish if you don't go steel)
My $500, 91-gallon RDS tank from Northern Tools can be used for either. It has ports on the top and bottom for either connecting it to the truck's fuel system (bottom port) or to install a fuel transfer pump and hose (top port), or both simultaneously.
In my case, I use the tank's top port with a 13-gallon-per-minute fuel transfer pump equipped with two filters and a gauge to keep up with gallons being pumped.