Hm that is a hard one i for one think that 50.00 is alot of money for a rabbit that someone doesnt want anymore, and find it hard to think that they arent trying to make a profit off of the rabbit. But on the other hand people make an adoption fee to "try" to ensure the safety of the rabbits, to make sure that they arent going to be snake food, human food, or bought for the entertainment of torture.
I guess it really depends on if you want this particular bunny? Beware that with things like craigslist and freecycles you are not garunteed a healthy rabbit with no problems. So make sure that you thoroughly check out the rabbit and know that you are risking that.
On another note i got my Belle off of craigslist and she was just fine, has the dutch attitude, but other than that she is great, so they all arent bad. The people who i got her off of, besides telling me she was a he,lol, they were charging 20.00 adoption fee, but after corresponding and them feeling that she was gettin a good home they never took the 20.00, which we had and were ready and willing to pay for her.
Good luck and email them and see where it takes you
Oh and another thing be careful when meeting people off of craigslist, or anything like that. Take someone with you, try to do a phone number search to see if number and name match up to what they give you, stay safe and let us all know what you decide,