Body work and painting always seem to be more expensive than customers anticipate.
Let’s just say that this type of work doesn’t come cheap nowadays–if you expect to get good-quality workmanship.
All of that being said, I believe that the OP has underestimated just how much work is entailed in getting down to the bare metal, smoothing the metal, repairing the dent, priming, and repainting.
A bill of at least $1,500 for this work doesn’t surprise me at all.