Take a survey of your area, and see what people of similar qualifications are charging. It will give you an idea of what the local market supports.
That's a good idea, but I'm not sure how you'd do it. It is not as simple as driving around looking at the signs for gas prices.
Interestingly, the AGO (American Guild of Organists) lost a court case this year about setting standard rates a professional organist could expect to get for performances like a church service, wedding, funeral, choir rehearsal, etc. The court ruled this was illegal price fixing, and forced them to take the rates off their web site.
If you have gained an additional qualification then it seems an opportune time to reconsider your prices. It doesn't look such a big hike to me, although I'm not sure what kind of $s you mean -US or otherwise.