Please someone put me straight if I am getting confused - which I may be.
Have just got back from Tesco and they have Schwartz herbs/spices refills that are around £1.28 each but are on offer as 3 for the price of 2.
Inside each refill box is a 50p voucher for some other pre-prepared stuff that Schwartz sell.
If I'm not getting confused, the vouchers inside can be used in Tesco for anything which would bring the unit price for 3 refills to around 35p(ish). 2 x 1.28 - 3x0.50. (you would obviously need to use the vouchers on your next shop, but it's all there.
This all hinges on whether you can use the vouchers even if you don't buy the items they are intended for. If you can't then please ignore :)