It depends if 50 dollars and hour is worth your time. I would definately make sure that you get at least some of the cash up front, and don't deliver the source code until you are paid in full. Always do the development on your own server and let them test it there. Once they are satisfied, and paid in full, then you give them the source.....
About the 50 bucks an hour...like I said, it really depends if it is worth it to you. Personally, yes 50 dollars and hour is worth my time. Think of it this way 50 dollars an hour at 40 hour weeks is a tad bit over 100,000 a year....