Finding the Price List associated with a Contract

When I change the Contract under Customer Billing Details on a Work Order, the line items I can add and their prices change. This seems to be driven by different Price Lists, so I'm trying to figure out which Price List is connected to a given contract, using the API. I've looked at PriceList and PriceListItem and Contract entities but I don't see how they're connected, so I'd appreciate any guidance on what I'm missing. Thanks!