single entry visa for china

I have been told by an agency that I will need a 2 year multi entry visa to visit my sister in China. My stay will be from 29/4/2016 till 1/6/2016 (around 30 days). The cost would be £185. Is this information correct? as I only paid £85 last year for a 2 month visit. Should I still be able to get a single entry one and do you know how much that would be