I agree whole-heartedly with dunster.
I go to 2 retreats a year at a Christian Camp and the food is prepared for us, so all we have to do is bus our own tables. The most we would have to share a bathroom with is 4 ladies (two separate bedrooms with a bathroom and shower in the middle). Since you know all of the ladies (anywhere between 20 to 35 ladies) it works out pretty well.
In order for me to enjoy a retreat at a house, as you described, the cost would have to be very minimal, as I don't see very many advantages to staying there.