I don't really think there is an "easy" or "cheap" way to add power steering to a straight axle truck. Guess it would depend on the capacity of your wallet.
One solution, which I happen to like and plan to use when budget allows, is the Rack and Pinion setup by No Limit Engineering.
Link: POWER STEERING STRAIGHT AXLE-No Limit Engineering (scroll down under size/color for the 61-64 setup). Cost is $599, plus you will need to buy a power steering pump and either replace steering column or cut your current column off in order to hook up the R&P to the column. (How to instructions are on the site). Note: If you have a Y-block, you can find PS pumps fairly easily, if you have a 223 I-6, PS pumps are almost impossible to find (unless you can fabricate a bracket).
Others have used a Toyota box but I don't know much about that setup.
You might first try making sure your current front suspension is in good shape (king pins/bushings, tie rod ends, steering box, alignment, etc.) before you make the PS change. You may find that by tweaking the front suspension (which you will need to do to have a good, safe setup with the R&P) you will not need the PS (or maybe not need it as much).