I'd like to point out that OP
@Cherokeekid88 just bought a used Tesla. I'd bet my hat this is for his charger.
There's more to this than just voltage. How many amps do you need? Hence what ga wire? Is there is a special kind of plug? Will this plug on the other side of the wall from your box be in the right place for plugging in the car?
With only 3 open slots and you're about to use 2 of them... how is the rest of the power situation in the garage? If you're running a heavy gauge wire for 240 anyway, is it worthwhile to make it a 60A and put a sub panel on the other end in the garage and be ready to tee off your charger line plus a few more 120s later? Its hardly any more work, all the PITA work will be running the wire, not the hookups.
OP came here asking about the cost to have this done by somebody else. IMO he's on the right track. This isn't a hard task, and would definitely be a journeyman job for an electrician. I'd do it myself w/o thinking twice but I've also cumulative spent weeks of my life reading code and years building up comfort - my impression is OP has no experience doing electrical and IMO running a 240v isn't the place to start DIYing. There's a lot of little things that matter to do it to code.
IMO best scenario is to find a knowledgeable friend to pay and do for you and walk you through it, or just pay a local guy and politely ask if you can watch what he does so you can understand better.