wrt to CRM. Try to consider the $50 as an investment. You only need to add X paying subscribers in one month to get a ROI. If you get them, then anything after that is profit. If you don't, then you have learned a nice lesson for only $50.
wrt to pricing - just experiment - take my least aggressive suggestion - allow users to dismiss the notice. Or if you can, split test it.
I think one of the other commenters here is right - you can probably build more of a sense of community around it. Perhaps it can be the place where people really recommend good books for language learners. You already have the voting etc. That then maybe leads you in to the publisher deals, which I don't think would be as difficult as you imagine.