Back a few years ago, we charged $1.25 day, but had a contract that required everything to be paid 6 months in advance. If not, the deer were ours to do with as we saw fit. We also wove in a charge of $40 a handling (most often we waived this but it was a protection in case a boarder required us to treat and treat and treat and treat what we would consider a hopeless case). This was due to experience when we found ourselves suddenly handling a boarders deer 4 times a day every day for weeks- with very little time for our own animals. Plus, if the boarded animal was a health risk to the rest of the herd, it allowed a way out.
Hope that helps.