Is it your local exchange, or one you're traveling to? If the latter, ask the organizers for some guidance on the local scene. Also, are you DJ'ing late at night or earlier in the day? Outside on concrete or inside in a ballroom?
In general, I think setting any sort of bpm limits isn't a great idea. The feel of the song is more important than the strict tempo. However, you asked, so, without further input on the parameters mentioned above, I'd say, for lindy, at an exchange, aim for most of your set between 130 and 190 bpm. 180 will feel bloody fast when you're tired, you've been dancing a lot, it is crowded, everyone is sweating, and the floor is concrete.
At the local dances I DJ I try to stay between 120 and 210, with the occasional spikes to 100 and 270 (but everyone around here does balboa above 210). When I DJ'ed in Herräng several years ago (perhaps closer to an exchange sort of audience), I went a little faster early in the evening, and I stuck to the 120-190 range for the 4 in the morning crowd.
Also, read these threads:
Final thought: are you foremost a blues DJ, and is that why you are asking about a lower level BPM...? If so, I think a "safe" number is 120 or 130. If you're more snooty about your lindy, maybe 140. There used to be people posting here who would have said 170 or 180.
Final-final thought: the best advice is to watch the floor and adjust.