My opinion - don't tell the electrician that this is for a Tesla. Electricians should be charging for the supplies and the time/labor. If that was the case, then how can there be a "flat fee".
My house was built in 2007 - it was a cheap tract-builder / cookie cutter builder. I've got a single 200 amp panel. The electrician I called was a recommendation. I payed, for parts & labor, $375.00 for a Nema 14-50 to be installed.
This is with my panel on the outside of the opposite wall of the 2 car garage.
The electrician that made this recommendation was one of the two listed by Tesla...so there wasn't much mystery there, unfortunately.