Personally, I think the cost should be based on how long it takes to get the work done. Electricians will charge around $60-70 per hour. If it is a pretty straightforward job, the parts will cost around $150-$200, and add the labour costs to that (including about 1 hour for electrician to pick up the parts etc.)
That being said, my nema 14-50 charger plug was installed in my garage, around 15 ft from my breaker panel for $300 total, parts and labour. It was done by someone that I know, so I paid a little bit less, but it shouldn't be too much more than that (of course depending on how long the run is etc)
The parts cost less than $200, so if someone is coming out and charging a very high amount, what hourly rate are they charging? $250/hour?!!!