The expensive mats are nice, and move less, but will eventually bunch up under the peddle. If you are going to be a Sunday driver with only a couple thousand miles a year, it might not end up being a problem. If you are a daily driver or close to it, then I would consider some of the methods suggested herein other than the clamps. The clamps seem like a good idea, and maybe work well with the thinner mats to grab them, but they are hard to actually insert into the carpet and then hold the thick mats. I would consider one of the grommet/eyelet suggestions, or as the one guy did, bond something rigid to the back of it near where it folds upward to prevent it from being able to shift forward and bunch up.
I just sold my RT (85k miles on it, 80k of them mine), and went through a couple of sets of the thick mats after my original stock set went out, and only tried the thick mats, and then the second time, tried the clamps.
For my SRT, the stock mats I got came with a little kit with something akin the clamps in the sense of the part that you push into the floor carpet, but a much easier design, as well as a stud on the top of this piece that you snap the mat into. I have yet to have a problem with that, but only have done a few thousand miles with it, so we'll see.