Similarly, I re-read the start of The Hitchhikers Guide to the Galaxy a few days ago (free excerpt on my Sony Reader). This includes a scene where Ford Prefect goes into a pub and buys six pints of beer:
Ford slapped a five-pound note on the bar. He said, 'Keep the change.'
'What, from a fiver? Than you, sir.'
I initially assumed that the barman was being sarcastic, since I'm surprised that the total price would be under £5 in the first place, so there wouldn't be much change left over. However, a few pages later he buys 4 packets of peanuts, which costs him 28p. That's amazingly cheap by modern standards, so I wonder how much the beer would have cost. This book was first published in 1979; do any organisations (e.g. CAMRA) keep records of average prices?