With stamps, I've discovered £1.50 goes a long way!
Inspired by the book and Instagram feeds such as the one Matt mentioned, I have been buying a few stamps and the older ones are a lot cheaper than the newer ones. I picked up a couple of sets from the 1960s that were a few pence each, newer ones were several pounds (none of this is costing big bucks...)
The stamp dealers say it's because in the pre email era so many millions of stamps were printed they have never become scarce whereas, today, a lot fewer are made plus their face value is a lot more than it ever used to be.
It's been an interesting diversion from the posters, especially given the way the dollar has strengthened against the pound over the past couple of months, which has pushed up the price of every poster in the US for us in the UK.