The way I read Priceline's rules on Best Price Guarantee the $25 bonus only applies to Name Your Own Price purchases, not retail.
If you find a lower price on a retail side purchase Priceline offers to refund the difference or cancel the booking, but not the $25.
From Priceline's Help section:
How does the Best Price Guarantee work?
All published price Air, Hotel, and Rental Car bookings are backed by our Best Price Guarantee. If you find a lower online price for the exact same product and itinerary within 24 hours, give us a call and if you qualify, we will either help you cancel your booking so you can rebook at the lower price, or we will refund 100% of the difference.
Click here for the complete Best Price Guarantee terms and conditions!
All Name Your Own Price bookings and Vacation Packages are covered by our Big Deal Guarantee. If you find a lower online price for the same exact product and itinerary, we will match that price and give you an additional $25.
eta: I posted a link to the above but it didn't work so I deleted it.