you do not need an extended length shock with a BB lift, however as billzcat has put it you really need them as the shock isnt damping at the intervals it was designed for and with thus get less than half the lifespan out of them. your better off with bilsteins, look at this last thread where like 8 out of 10 people said bilsteins. including myself.
however yes the will set you back about $300
check ebay believe it or not they are $250 ish for bilstein HD's for 2" extended length. or kolak will set you up with 5100's or 5125's. i have the 5125's rear and 5100's front. paid about $300 as well though. wouldnt regret the ride.
but here is the other thread in which i was talking about