France's requirement for breathalyzers in cars

I've noticed this morning that a well known Caravan accessory retailer is advertising these alcohol testing kits for cars at £4.95 for 2.      British buyers may think that is cheap but they are available here in France for 85 cents (about 68 pence) each at any pharmacy.    Is this another example of retailers charging what they think we will pay rather than what an item is worth???