How much are these rare postcards/postcards worth?

I was watching an antique show on the television the other week (here in the UK) and someone was selling postcards such as the one you have. They reached quite a few hundred pounds, you would need to check with an antique dealer or auction room in your area. They might not all be worth a lot of money, but there could be the odd one or two that might raise the price of their worth.