Using air shocks or coilovers can easily double or triple the cost of linking a suspension. Nothing to sneeze at.
I'm still using TJ coils in the rear of mine, I have 3 sets that I got for free with little/no effort (two of them were brought to me). It couldn't possibly be easier to find spare or replacement springs than that.
Now, of course, they're not the ideal option. Basically, coilovers are. But they run $500 a set.
My suspension works pretty damn well with free springs and $25 shocks.
I will be almost certainly be going to coilovers before next season but it will be to replace the leaves in the front before it will replace the coils in the rear.
Cheap coils CAN work just fine, you just have to find a set that has the length and spring rate close to what you need.