I did a REU this summer (the program was a combo of all disciplines) and all I can say is :
Despite my experience, it was a good program over all. 3k, GRE prep course and test, great workshops, work experience and covered housing.
If you really love research, go for it. It's great that you are starting now. Take a week to ust google "REU"s and also use the search function to look at old posts on this board that discuss REUs.