I'm sorry to tell you that many one-to-ones are quite expensive...they range from $80-$90 per hour at least. However,I would still recommend you to use these following websites to search for one-to-one university tutors. Satisfying your needs, here are some of the websites of university tutors and professional tutors recommended to you:
www.ututor.com.hk
This web page is the best (personally)
www.tutorabc.com
(This is a web whose teachers are of great academic background and are teaching at a very low price!)
Hope i could help