Should be anywhere from 30–60 US dollars.
You might be able to order one off Ebay or find one at a junkyard for cheaper.
I found the starter for my car at a junkyard, and payed $5 for it. It hasn’t had a single problem.

The part will be the least expensive part of the job. Usually the labor is at least twice the cost of the actual part.

To have someone else replace it will probably run about $300 or so plus parts. To do it yourself you would have to purchase a starter. This site shows that they run from $90 for rebuilts to as high as $131.52 for the SL.

Before you go out and get an estimate on a new starter, bang on it with a hammer a few times. You might just have a stuck solenoid. And, of course, check the fusible link between the battery and the starter motor.

Thanks to everyone that helped! I managed to get a part for $130 and labor for $25! Towing was an additional $70, but I don’t think I did so bad.

@Lacroix thanks for the update