Mihail,
Sorry, I forgot a part:
Query1:
Select ID_Product, PriceDate
From tblProductsPrices
Where PriceDate < Forms!SomeForm!TheDate
Query2:
Select ID_Product, Max(PriceDate) As TheDate
From Query1
Group By ID_Product
Finally:
Select A.ID_Product, B.TheDate, C.Price
From tblProducts...