I had a similar problem when I moved into my house. The house was wired for 120, but everything I own is 110. I ended up having to hire an electrician to re-wire the whole house to comply. Electrician was a little hesitant at first, but once he got the 50% down check, he went to town. I was really impressed with his work. He said we couldn't be in the house while he did the work since there would be no power while he made the swap. Understandable.
He did so good that you can't even tell he did anything. Luckily he was able to reuse all the outlets and switches, and he somehow patched all the drywall and had it painted so well, you would never know anything ever happend. He even drew back on all the drawings in crayon my kids so kindly left on the wall too!!!!
While we were out of town while he did the work, he kept me appraised to his progress. He did say that he needed to remove some of my things as they would no longer work with the new voltage in the home, and apparently they were illegal to have in the house. Something about a code or something.
No biggy though, just my TV, blu ray player and 2 year old surround sound system. I had a huge chunk of money in those, but better be safe and not break any codes, so I let him take those. I've been known to be a little on the cautious side.
I'd reccomend talking to an electrician about your problem. Usually the ones in the Home Depot parking lot looking for work are the best since they aren't a big company with a lot of overhead, so their prices are usually cheaper.
My electrician had so little overhead, that his van had his logo painted on the side. He said he did that himself just to keep costs down in his company so he could pass the savings on to his customer. Don't go the big companies, they will bend you over the table.