Erik B started a provocitive thread about this on the Pirate Bulletin Board a few years ago. It really depends on how extensively you want to modify your truck. If you have big plans, the truck will end up more or less the same regardless of it you start with IFS or swap in a solid axle. In an 85 and older truck, you need to add an IFS steering box and later, wider rear axle. These two items will cost you somewhere around $300. If you start with an IFS truck, you already have these items but you need to get a front axle, which will cost you somewhere around $300. The other expenses are the same, like lift springs, lockers, gears, dual transfer cases, etc.

The ONE thing that this does not take into account is the shape of the front frame rails. You can run approximately 2" less lift on a solid axle frame and still have room for high steer components due to the shape of the frame. I think that this is enough of a feature to make me look for an older truck.