Printing a poster near a conference location at a cheap price
First off, avoid the print shop at any conference location, which is quite likely to be both overbooked and expensive.

Second, make sure to send your poster far enough ahead of time to avoid a potential last-minute rush (particularly at large conferences).

Finally, you can use Internet map sites (Google Maps, Apple Maps, etc.) to search for copy shops near the conference location, and call to find out their rates.