Suggesting there is any reasonable expectation in general is really not at all possible. Find comps for products that are the same or similar, check out their prices and find out their conversion rates. Only then can you start to formulate a reasonable expectation for your specific product.
If you provide good support and listen to their needs, 10% is not unreasonnable but giving good support can be very hard, depending on the size of the community.
I would use 1% as a basis -assuming the service really serves a need- and go up from that, depending on the available resources for support.
10% would be on the low side if you've got people actively using your product to improve their business. You can easily hit 100% adoption by droppping the price for active users lower and lower till they all adopt.