The problem there would be your breaker. I am not an electrition but I can tell you that when I tried adding a heated MAU to my house, I had to switch to a 120v washer/dryer because my electric panel did not have space for another 208v line.
(Note, my building is actually 3 phase 208 volt not 240volt so I don't have 240 volt plugs but 208volt plugs)
Not a criticism, but a question. Did you consider adding a subpanel? If you're running a new circuit I assume there was already some drywall patching to be done, seems like it would have been more cost effective and removed future headaches to just give yourself more breaker space.
A lot is going to depend on labor rates for your local electricians, but that costing more than $500 where I am would be outrageous. I do my own electrical, but even I paid a licensed electrician to come handle installing a new panel since I did not have an outdoor service disconnect and didn't feel like fighting with the utility company over de-energizing and re-energizing my service. Ended up needing a lot more done, but the whole thing cost me $2500 to get a new service drop, outdoor meter main, and wiring run to the old panel (in the bedroom on the other side of the main) and the new panel (in the old furnace closed that's now my electrical / network room).
But really, doing a subpanel yourself to expand breaker capacity is a really simple project - most people if so inclined could do it themselves. Anywhere from $100-200 for the panel itself depending on how many spaces you feel like adding, up to $80 for a large enough breaker to feed it, and some tens of dollars for SER cable.
Agreed - I’ve ended up installing 4 (inspected) ones over the years myself, and one I paid an electrician for (they also had to upgrade the main service feed).
IMO, what usually drives up the price is the ancillary stuff - opening up a wall (and re-finishing it) because there isn’t enough physical space, or adding extra main panel capacity/service capacity because the main feed is insufficient, or having to run heavier than expected wiring because the only available space gets really hot (poorly ventilated attic space), or having to run surface conduit due to a specific challenge with framing.
Then add in labor (where I was in a high cost of labor area), and it can get expensive quick.
An actual surface mount subpanel and appropriate wires/breakers is usually only a couple hundred bucks total like you note.
(Note, my building is actually 3 phase 208 volt not 240volt so I don't have 240 volt plugs but 208volt plugs)