How much is normal to reduce one's rate from FS for FBSM?

It is time, after all, that is paid for.

I few however do, and I would say the average difference is about 25%, give or take.

Where I am I would say it is a good 50%.

In my area FBSM is considerably less costly than FS, but there's a lot of variance between providers.  You'd have to say they set thier prices according to how they run thier business.  I think there is more variation than the average "base" FS price per hour. Some as low as half.  There's a lot of variation in technique so it's hard / unfair to compare...   Also there's the question of her appearance, what is on the menu for an ending, etc.  Larger donations don't necessarily get you more or better service.
I would suggest you search names & phone numbers (separately) as massage & escorts here to see if you can get an idea as to the quality of service.  Do your home work.  Then, there's nothing else to do but sample the buffet.  DO write some reviews.  
skb