much should this cost, roughly? I also need to have a fuse upgraded from 15 to 30V. I know it will depend on the amount of time, wiring, etc., but any ballpark idea before I get estimates?

... it's tough going on that, depends on your framing and how far the plug locations are from anything else in the house electrical, of course they'll have to tear out the walls and insulation to do this, I would say at least 600-8000 per outlet if I had to guess. Extention cords are much cheaper, I'm not sure but I think upgrading a fuse is not a big deal maybe another $50.

of course this is for an electrition/contractor to do it, not yourself

You need an Electrician. Not a Handy Man!
If you were having a heart attack would you call the Vet.?
Get a Licensed Bonded Electrician.
Most Electricians will give you an Estimate.

Definitely cheaper than a ballpark.

OK, there are way too many variables to even estimate this, but let's say you have a basement with an exposed ceiling and an easily accessible breaker panel. If you can freely install conduit along the basement ceiling from the panel to the exterior wall and drill directly out of the basement wall to the two receptacles....under these circumstances.....$200 to $300. If you don't have these circumstances, then assume that you will pay more. You will be better off calling a licensed, bonded, insured handyman service than an electrician. The only way that a handyman can screw you on this one is if he tries to talk you into tapping off of existing outlets when he isn't sure if the existing load of that circuit.

Hourly rate for two electricians, plus travel time, plus parts and materials... It ain't gonna be cheap! Figure several hundred dollars to start and go up from there.

I assume you mean 15 to 30 amps you must make sure the cable is of sufficient size to take the increase in current remember the principal function of the fuse is to protect the cable from overheating generally speaking you cannot just replace a 15 amp fuse with a 30 amp with out putting the installation under stress the system may appear to work but you could greatly increase the fire risk