I've lost count of how many times I've typed this on this website, but:
you're worth whatever you can negotiate.
I have negotiated as high as $450/day for a DA40, $400/day for a Mooney Acclaim and as low as $200 when I was a bit younger and needed the cash. It just depends on what you can negotiate. This may sound crass, but I firmly believe that in the aircraft I specialize in, I am the best pilot that somebody can hire. With that, I demand what some would consider a high daily rate. If people complain about a hundred bucks, you probably don't want to be flying their plane anyway.
Also, if you have to travel, make sure you get some sort of agreement that if you get there and the plane isn't up to par or something that you still get your money. This is important.