paul,
congrats on the tub.
approx cost per foot is aroud $6.50-7. if the run is over 100 feet, it would require an upsizing of the wire, that would be about $1 more/ft.
anouther charge would be for a disconnect. you can get 1 at lowes/home depot.
"Should I have an electrician already run power by the time the spa has arrived"
you could, but see how fast the electrician can get back out to do the hook up if you did it that way. also, if there is alot of trenching involved, it might not be a bad idea. however, if there is minimal/no trenching, it wont be a big deal. you could always ask the electrician what he thinks would be the best route for your hook up.
only other advice would be to have the tub filled by the time the electrician is done with the install. that way you can fire that bad boy up right away so IF there is a problem, the electrician is there and can trouble shoot if needed.
happy soaking
socal