Still, how did you know the lower ball joint was going bad?

My point about the cost is it will cost more than you think. Do your research before you start a SAS. Do you just want a solid axle in front, or is the goal that you actually want to go off-roading with it on some very tough trails? You'll need gears to match the rear and maybe a front locker (less cost to only install the gears once). Which front axle you choose will determine if your stock transfer case will even work. Or maybe you want lower gears so you want a different transfer case or a dual transfer case, then you might want to save some money and only buy one custom driveshaft and do it all at once.

Since you have the un-flexy torsion bars on your 2nd gen 4Runner, I can understand your desire to have a better front end and do a SAS.

Depending on what kind of trails you want to do, unless you want to get good at replacing U-joints or birfields, you better look into durable axles and joints. It doesn't look like you're doing this for the purpose of improving flex and off-road capability on really tough trails, so yeah, maybe a lower cost SAS is reasonable for your goals. My cost info comes from seeing several people do SAS's for the purpose of doing very difficult trails. Of course they go with much larger tires too.

If you wanted more flex as well, you might consider a coil-over SAS kit, such as the one at http://www.offroadsolutions.com/products/suspension.htm#tacoma_coilover_systems
But I'm just assuming that that kit might work on a 2nd gen 4Runner, which I don't know. [Edit: I see they have a similar kit specifically for other older years of 4Runners.]

There's a Toyota SAS cost thread here:
http://www.4x4wire.com/forums/showflat.php?Cat=&Number=976104

From what I've seen, it's difficult to keep vehicles reasonably low and do a lift for a SAS. The best-designed SAS I've seen that's still reasonable low is: http://www.houlster.com/amigo/SAS/