This is one "sticky" subject with pro's! On one side you want to help them out, on the other side it's hurting the pro's every time someone either doesn't charge for photos or just "covers expenses". I personally wouldn't touch that deal for less than $250.
Consider that they want the photos to promote their business, ie, to MAKE MONEY! So, in reallity I would probably charge them more like $500.

Just some things for you to consider.

JS