I have heard of a couple methods for removing rust from rattling a chain/sand/rocks with diesel fuel in the tank to doing an acid treatment. Is this something I should attempt to do, pay for a professional repair, or just replace all together?
Motorcycle folks seem to do this a lot, presumably because the gas tank is easy to remove and small enough to manhandle (personhandle?).
A Google search produces a lot of results for how to do this, and any of the ways you've heard will probably work well. Here's one detailed list: http://www.mopedarmy.com/wiki/Removing_rust_from_a_gas_tank
You have to decide what your expectations are. If you just want to remove a lot of rust and be done, use chain / rocks / screws / ice cubes. If you want a pristine gas tank that will resist rust for a decade or more, you'll want to get ALL the rust out and then coat the inside so it won't rust again. In that case, try POR-15.