Weddingbee boards

One of my BM's is getting married tomorrow and I spoke with her about an hour ago, and since she's not living in the state, planned the whole thing destination to be in her home town - I offered to help, and to not hesitate to ask if I could do anything.

When I did this I was expecting set up help, things like that. Since it's a private ceremony only family (about 10 people) will attend and the reception hall has everything taken care of initially she said she didn't need anything but then said she may call me in the morning to dirve her in laws from the hotel, to the salon to the reception venue - in total about 80ish miles and I may have to do this more then once!!!

I don;t think that I can do this - finacially anyway. It costs near $65 to fill my Jeep and I have NO money as is right now.  I mean I was scrapping togheter cash to buy something that fit me to wear to the wedding in the first place. And we still haven't got her a gift!

I don;t know what to do - she has no one else to do this for her or she woulnd't be asking me. I feel horrible saying "I'm sorry I can't afford this" and when I say that I mean like I can't even front the money to put in the tank to get to her to get a check....it's been and extra tight month, normally this woulnd't be an issue...

What should I do and how should I do it? I'm so confused. 

HOw should I say it though, with out sounding like I'm looking for a hand out of sorts, you know? I offered to  help, so expecting to be compensated is considered rude...isn't it?