Seems that aftermarket leaf springs are in the $1,000 and up range. If they put new leafs on both ends, that would eat up a lot of that estimate. Then the cost for the front hangers, mods to the existing front axle, and new shocks since ride height would be changed, seems the estimate is low. If they only put a block in the rear and don't change out the shocks, then it seems it could be doable.
2005 E350 Chateau - V10 - Agile Offroad 4x4
2012 CTS-V Wagon - For the baby...