Best and cheapest shocks you are looking for are OEM take offs. Stock take off shocks are ideal for what you're planning. Any stock shock from an 03-09 4R or 07-09 FJC will bolt right up.
If you don't mind doing a very little mod you can run (easier to find low mileage) 2010+ 4R shocks. These are officially the Prado 150 and as far as the suspension mounting points go everything but the front lower strut mounts are the same. The lower strut mounts are 1/8" wider on the newer trucks. SO if you remove 1/6" material off both sides from the center bushing sleave of the lower mount on the strut it will mount right up to your GX. This is not modifying your car, just the used struts.
The difference between the Prado 120 and 150 is so slight that all the big suspension brands just ship everything set to 120, as it installs just fine and the mounting ears snug up when the primary bolt is tightened down. You are doing the reverse but just grinding a small amount of that center bushing sleeve on each side.
Post up in the 4Runner forums for your area your looking for low mileage stock take offs. Some guy that put a $2600 ICON kit will have his sub 1k mile full suspension in a box in your area. You want the WHOLE suspension including the rear springs from him. I would not pay more than $350 for the whole thing as there really is no market for used low mileage takeoffs. The other advantage is this way the front struts come with new OEM coils as well, already mounted on the struts. This makes the install crazy easy. You also get OEM Toyota rear coils.
As the company that invented the rear coil conversion kit, we appreciate you buying the original! Just use our stage 2 kit with that takeoff suspension and you're golden.
Metal Tech GX470 Rear Coil Conversion Kit Stage 2 w/OEM Toyota Parts
Mark