If they're just throw-aways, drop them off at Wal-Mart or Walgreens.
I'm not really sure how much a pro lab is going to help, since the developing of the film is all the same regardless of where you go (c-41 is standardized times, temps, agitation, etc). The pro lab will probably take more care against scratching or exposing your negatives before/after development, but that's probably about it.
I could be wrong, but I don't see a big reason to go to a pro lab to develop negatives. Prints are a different story; they're more likely to take the time to examine each negative and with an eye that has years of experience make a darn good print.