Hi Robert!
First of all, congrats on becoming a new music transcriber!
Rates and fees definitely vary depending on many factors. Different transcribers have different expectations, expertise, and experience levels that affect their rates. Some transcribers work as volunteers and some are transcribing as a career, so it's hard to generalize and feel confident in giving you a definitive answer. My response here should be taken as simply my personal opinion and what I've seen in the field and not as a definitive declamation of how much transcriptions should cost.
For straight-forward music, (single-line music, line-by-line vocal, piano, etc.) prices tend to range from $7.00-$10.00 per braille page. It can vary depending on how fast you work - if you can get it turned around in a short amount of time, the rates can be higher. If it takes you 6 months to get a single-line piece of music to a client, I'd probably recommend lowering the fee.
More complicated music can be billed at a higher rate - music that uses non-traditional notation can cost between $12-$18 per page - again also depending on the level of expertise and time it takes to get the work done.
Proofreading tends to sit in the $2.00-$3.00 per braille page range but also depends on speed and accuracy.
Again, these rates I've quoted are merely my experience in the field and shouldn't be seen as "this is how it should be for everyone." But I hope this gives you some sense of what is out there right now and what you can expect moving forward with your transcribing!
Congrats again!
Kathleen