I had my front and rear bumper guard holes filled, along with new chrome on front and rear bumpers, and new chrome on the 2 pieces that sit on the soft top lid, cost was $1,100.
In addition to the cost variables that Richard mentioned, other variables would be the process itself... copper, nickel, chrome, nickel, chrome, etc... (# of each metal type) and how long the pieces are held in each of the tanks allowing more of the metals to adhere.
I would think that you need to be careful redoing small pieces in that they may not fit well together again. Some of the good resto shops will do dry fitting at the copper stage, then sand the copper to fit... then dip and apply chrome, etc...
Bob
bpossel (Memphis, TN.)
'71 280SL / '97 E320