I recommend IOU as well. I go to the one in Causeway Bay instead of Mongkok but the prices are the same and I find the results very good. I've tried a straight perm and a body wave perm and have been very happy with the results!I go to Mongkok branch of IOU salon the 3 times I have been back to Hong Kong. Can google them. But I have never spoken English to them.
They do a good job and it's cheap enough that I don't bother trying cheaper ones. The basic price is $220 for straight perm. ~$400 for perm, cut & color. But I always "upgrade" the chemical (between $100-$400 more, I always just choose to upgrade $200). So in the end it's ~$600.