Hi,
I dont know how much they charge, but this system of charging an annual fee seems to be the "norm'. I have tried to find an agency which charges a percentage of the rental fee, rather than an annual fee, but with little success. I feel that if they are on a percentage, then they are far more likely to promote your place, than if they take a fee each year and sit back.
If they are so confident that they will get rentals - as they all claim - then why not work on a percentage basis?
John