In lots of 25, the 'dip this paper' one costs 50p each, inc VAT. The 'works with stored urine' one is £1.

If you've ever bought one over the counter at the chemist, you probably remember them costing Rather More Than That, albeit in a different form ('hold this pen-like stick in the flow of urine' is the type I've seen, avoiding the need to pee in something).

I'm tempted to order a pile for sale, at cost, at somewhere like BiCon. They claim a shelf-life of about two years.