Do you already own 4 CLS compatible SB's? (ie SB600 or SB800) If you do - then getting the SU-800 is an option - but slightly limited in that the remote works via IR, so you'd be limited by available line of site between each individual unit and your source unit.

Have you thought about getting the bullet proof set of pocket wizards? Might be more expensive, but you can buy used non-CLS SB's for under $100 (like the SB-24 or even the Vivitar 285HV)

I'm thinking about going with a "poor-man's off-camera flash system".

Ebay sells used Vivitar 285HV's for like $30 each. (Just think, for the price of ONE SB-600 - you could get like FIVE used Viviars) Then pick up a couple of "ebay radio slaves" for like $40. This won't be as reliable as the pocket wizards - but they should work in alot of environments without limitations of line of site and without the costly price tag of the pocket wizard.