You don't actually need the PriceDateEnd field.
You can't look this data up into the Product table as it does not have a date sold field nor should it. I will assume that you are looking up this price in a LineItems or InvoiceData field using the typical Invoices---<LineItems>----Products data model.
Set up this relationship.
LineItems::DateSold > Price::DateStart AND
LineItems::ProdID = Price::ProdID
Double click the relationship line for this relationship, click the sort button on the Price table side and specify a sort order that sorts the records by DateStart in descending order. The first related record in this relationship then becomes the most recent price where the date start is on or before the datesold.
You'll need to set up LineItems::DateSold to auto-enter that value from a date field in your invoice table.
With this relationship, your LineItem (or InvoiceData) table can auto enter the correct price based on the data the item was sold. Past and future prices will be ignored.
Worked great! I appreciate it, never would have figured out that solution.