Within a distance you can walk, it should be pretty easy to find a band with minimum interference even in a crowded metro. Also, quality won't be as much of an issue as range. There are pretty low limits on how much power you can use on the FM bands without a license.

Source: I drove all over a crowded metro in the early 2000s with one of those fm transmitters for playing audiobooks to my shitty car stereo. 3 station presets was enough for the whole area.