Amazon.co.uk offers Police Academy: The Complete Collection on Blu-ray for $21.07 (£13.40). In-cart, that drops to $17.57 (£11.17). With $4.84 (£3.08) for shipping, that's $2 under our October mention and the lowest total price we could find by $2. This set includes all seven films and behind-the-scenes features.
This Blu-ray set is region-free, and the films themselves will play on US Blu-ray players, but note that the extras and special features may not.