Look at the plug/tag on your hairdryer and there should be a voltage range. If the highest number is 220 or up, then you don't need a voltage converter. I bought a voltage converter/adapter set at Bed Bath & Beyond last month. I think it cost around $16, though I had a coupon so maybe it was really $20? The adapter plugs work for all countries.
If you don't know what voltage or plug the country uses, look here:
Electric Current Worldwide (ECW)