from what I have found, with as cheap as these older f150s are no reason to settle for a rust bucket.. Personally I do not see the point in repairing it when it gets to this point, my time is worth more to me. But I guess you decided how much your time and the cost of materials adds up to and decide if its worth it to you.
Also think, I am sure more than just the frame is rusted out. Hows the bed, or the car floors?
-1993 F-150 4.9L 4x4 Automatic
Bought 08/03/10, its lifted and has 35" tires other than that I dont know anything about it haha!