Sudden fee change

We hired a doula through a mutual aid society (“gmach”), where this service costs 300 NIS for a weekday birth. When we asked, how much the service will cost on a weekend, the answer was 1000 NIS. The birth took place on a weekday, but the doula said that we have to pay her 1000 NIS. When the husband expressed his astonishment at this price, she explained that what she really meant is that if she only has to be prepared to handle the birth on a weekday, then the price is 300 NIS. But if she is on alert on a weekend as well, then the price is going to be 1000 NIS anyway (even if the birth actually took place on a weekday). That is, in this case, there is no “mutual aid”, they have to pay the full price. But what the husband understood originally is that the price depends on when the birth actually takes place, not on the intentions and preparedness of the doula.  

If this is the way that the fee is determined in all such “mutual aid societies”, then the husband has to pay her the price that she asked for, even though that’s not what he understood. The reason for that is that, if this is the market price, then he should have known that. But if some doulas price their services this way, and some don’t, then she should have explained herself clearly. And now, that she did not explain herself, the husband only has to pay her 300 NIS, since he had no way of knowing what her pricing scheme is.  

Shulchan Oruch, section Choshen Mishpat, chapter 331