I have the R-540 which is inexpensive and not that much heavier. But if I had to do it all over again, I woulda went 105 or ultegra because of the metal top plate. The 540 has a plastic plate that I can see is getting worn down. It will probably take a while before they're destroyed, but I'd prefer the metal plate on the 105/ultegra pedals.

Nashbar almost always has the r-540 for $40 it seems. Very good value if money is tight.