The less she's inclined to do it, the more she's going to charge for it. The question of value is up to the individual buyer.

This plate will set you back about $10.00...

for four days in Santorini.

see if they allow Greek.  They may have a higher rate for FS + Greek than for just FS.  From what I have read, it seems to be around 100-150 extra for Greek, but I'm no expert on it.  I think doing the research I suggested will give you some idea as to an average add-on.

Swim