Possible Clues:

• . . . in a Main Street shop
• Change-machine insert
• One __ (change-machine insert)
• Its back features the last parts of 17-, 26- and 44-Across
• Tip jar insert, perhaps
• Three-__ (phoniness symbol)
• Single buck
• Vending machine insert for one?
• Its average life span is 22 months
• Change-machine input