I think my Fox shocks were 750.00 for the shocks and 150.00 for the springs. The RCD kit was about 200.00 for all the mounts, etc.
The coilover might get you an inch if you rally crank up the preload, but your ride will be very rough. The main thing that I was suprised to see was that the ST and all Explorers only have about 6" of travel.
I was in the same boat as you, I did not want to cut up my ST or have to park it for a long time to do the work. I finally had enough of destroying my tires every year that gets expensive real quick replacing 33's annually. The alignment sucked no matter who did it, and I was always scared that the front diff or CV axle would break in the middle of nowhere. So I finally said that's it and started collecting parts for my SAS.
First was a junkyard Dana 44 from a grand Wagoneer, that was about 150.00 then I just started getting everything together, to completely rebuild the axle from rotor to rotor ( the list is very long). I used alot of high end lifetime warranty parts ( ARB air lockers, CTM u-joints, USA made Superior chromo axles, all MOOG parts, Blue Torch fab, and Ruufstuff metal parts), Wife was pissed and she still does not understand what I did to my truck, but I know and others who see it and then do a double take and lean over to look under know. I always get a thumbs up, and a shit load of questions and comments.
Here are some links to my build thread and SAS registry: You will see I asked ALOT OF questions from those who done this.
http://www.explorerforum.com/forums/showthread.php?t=237526
http://www.explorerforum.com/forums/showthread.php?t=254382