We initially geared our site towards teachers, but later learned that wasn't the market that was willing to pay for our services. Maybe your experience will be different.

It is a slow process. About 1-2% of our customers convert to paying accounts. When we started limiting what was free it seems people stepped up to the bat and subscribed to a paying account.

Note - your prices seem very low. You could experiment with your price structure, people might value your service more than you realize.