I've seen posts in here noting that cruise control on long trips helps with gas mileage. I have the base model Prius, which I love. I haven't wanted for the things with which it was not equiped, except for that cruise control and the cargo cover in the back, which I already got off of Ebay (honestly, I was a real dough-head when I bought the car because I thought it had cruise control on it - didn't realize it until I got home). Anyway, I would like to add it at some point in the future. Has anyone else done this? Would it be ridiculously expensive to do so?