Don't forget your local grange as a resource for things.  At Capital City Grange #469 (the site of the Montpelier VT Contra Dance) we own coffee urns and carafes, coolers,  etc. and could recruit volunteers easily, I think, for an event like this.. 

When the Vermont Fiddle Orchestra played at the Northfield Farmers Market on the Common, they had a tent.  Maybe it was owned by the town?  I could find out.  In Maine, you have Fiddle-icious  and the Franklin County Fiddlers, both of whom would provide lovely music for dancing, and neither would require amplification.

The CALLER, on the other hand, should be amplified, in my opinion.

merry