Access 2003 - Populating a text field from a combo box within a sub form

I currently have a main form 'frmBOMtest' that has two combo boxes.  The first filters item classes, and the second box then would show the available parts with the class selected in the first combo box.  That selection is then added to the primary key field of the sub form, so as to tag what SKU goes with the parts that are going to be selected in the subform.
My subform has 5 fields on it.  
ItemSKU (PK, hidden)
DateEntry (PK, hidden)
PartNumber (combo box)
Quantity (control source is selected to 'tblParts')
Price (which is an unbound text box, relating to a separate table called 'Item'.)
When I select the Part Number combo box, I want the Price to automatically look up a value from the 'Item' table that queries the associated price with the item selected in the combo box.  The problem I'm having is that when I use an AfterUpdate command string tied into a listbox (no row source with text boxes?), it finds the associated price, but it updates all fields in the 'Price' column with the value I just picked.  Is there a way where I can just pick the SKU, select a part in the sub form, have the price show next to that part on that row, and then move to the second row and repeat?  (for as many parts as necessary, probably up to 15 for each SKU)

here is the afterupdate snippet I was using in an attempt to populate the 'Price' field on the subform, which I'm sure is wrong, but it gives you an idea of what I'm trying to do:Start Free Trial

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Private Sub cboSelectPart_AfterUpdate()
    Me.lbxPrice.RowSource = "select [Item].[Price] from Item where ItemNmbr = '" & Me.cboSelectPart & "'"
End Sub