Waterpumps of 560sl's are a bear to do.
I did mine myself-was quoted $1200 in Atlanta to do one. The pump is inexpensive, (I think MB gets $250 at the dealer), but you have to take all 5 belts off, and the harmonic balancer to get at the last water pump bolt. Not that hard but a lot of stuff to take off just for a waterpump. This topic has been thoroughly discussed-search on "waterpump."
I agree, a lot of $$$ but probably not out of line in relative terms.