Are cost estimates consistent and binding?

Friday is a neighbor on my coupe long rammed. Back left bumper and fender, fortunately only paint damage. Monday I had a cost estimate created. Look here. http://hometown.aol.de/guentherdortmund/page1.html In order to save the neighbour costs, I tried today to have the bumper repaired on the basis of the cost estimate “only” (Pos. 1005 for 8,50 € and Pos. 1030 for 23,- € plus shipment 87,- €) But a little. Now Fiat says, the Pos. 1010 for 200,10 € and the item 1020 for 184,- € belonged “in that case” to the bumper. So incl. fairytale tax 584,41 €. The neighbor is Stocksauer and feels fooled by me. Is an estimate not binding? Of course, your insurance also takes over the damage. But you shy away from the increase. Greeting, Günther.