here's some good reasons to stay away from quick fix paint & rust products, POR-15 & the like. Do with it what you will but for all the efforts & labor I've poured into my project I'm not interested in having the same problems, its just not worth the risk when there are so many other ways to do the project correctly.
http://www.spiuserforum.com/showthread.php?285-POR-15-QuestionJmac's right, it'll cost a fair bit in decent materials & with something that rusty it'll need a LOT of loving to get it straight, prepped & ready for a topcoat of paint - it will not come cheap at a body shop & if it does be wary! Think of it this way, anyone w/o any mechanical experience can turn a wrench & learn along the way w/o too much harm caused - paint & body's a totally different story & to get it right takes effort, a lot! You get what you pay for.
some of the paint & body experience & advice I've read here is suspect to say the least, let see...beer cans stuffed into rockers then bondo-ed on top of them, fish oil inside panels for rust protection, how does that help paint adhere to metal & you know its going to get on the outside of vehicles. You just cant cheat on trying to get rid of rust, cut it out & weld in new metal & forget encapsulating it. Surface rust- grind or sand it off then spray w/epoxy as a seal coat.
The fast & easy fixes will haunt you, do it right the first time.