What is a vendue? Why is it given to the lowest bidder?

A vendue is an auction. The bidder isn't paying, the town is paying the bidder. Admittedly, this is an extremely confusing concept.

The above will be put to the lowest bidder who shall board and nurse them in sickness and health and pay every expense for them except doctor's bills which the town will pay, and clothing which the town will provide. The contract shall continue one year from the first day of January 1793, when those persons who shall keep them shall remove them to the place, which shall next be provided for them if within the town of Jaffrey.

This practice seems to be similar to indentured servitude.