Instead of a label, you could use a text box with
enabled=no
tab-stop=no
locked=yes
so that it looks like a label. Then set the control source to be:
comboboxname!column(2)
This returns the value in the second column of the Row Source of that combo for the selected item.
I'm assuming here that the price is the second field in the Row Source for the combo box. For example, if you're selecting from Table1, then the Row Source will be either:
a Table1 (and the price is the second field)
b a select statement: e.g. Select field1, price from table1
If it is not then change column(2) to column(3) or whatever is suitable.