Column look-up in a formula, probably easy, but I'm lost

Hi all, and thanks for the help. I think this may be something relatively easy but am having trouble figuring it out.
I am trying to create a formula that would look-up data and return a value to a formula. Here are the specifics.
Dealing with storage costs of raw materials in different package sizes. In the attached you will see PACKAGE WEIGHT is in Column A and the corresponding STORAGE COST in Column B.
Elsewhere in the workbook would be purchase order lines that would include a PACKAGE WEIGHT per line. I need to create within my calculation a way to reference the PACKAGE WEIGHT in the purchase order line in order to somehow go to columns A and B, find the same package weight in Column A and return the corresponding cost from Column B into the formula. I will have about 20 package weights and about 3000 purchase order lines, so this will save much time and would allow me to analyze changes in Column B costs and their impact on storage costs over time quite easily.
Is this possible?
Thank you!