Hi Nige,
I guess that its not a huge "mess", perhaps worth getting the old filla out and smothing it over?
Then perhaps trying with the "courtesy" paint you would have got, to cover up the area?
I would have thought a little job on the bumper would "only" be about £150, as they would have to blend it in etc etc... (professionals)
making you think about parking sensors now?
I hope its cheap to put right... if not, just make sure now one drives too close to you
-drib