Try this formula in E2:

=LOOKUP(2,1/('Data Purchases'!$A$2:$A$17=A2),'Data Purchases'!$B$2:$B$17)

or

=LOOKUP(2;1/('Data Purchases'!$A$2:$A$17=A2);'Data Purchases'!$B$2:$B$17)

depending on your version....

Adjust ranges to your database range.