Depending on your budget, if 100 dollars is very much money in this case, I would say it could be advisable if you really need external mics (maybe even a few of them for stereo and different situations). One suggestion though is to look at the M10, a very popular choice, since it not only is of good quality but has pretty good and quiet omni mics suitable for recording ambience (although practically in mono). If an omni for ambience was on your list, then you can get the omni and good recorder in one package.
Others probably has more to say on the subject.