BBC Proms Arena/Gallery Ticket: £5
'Promenading in the Royal Albert Hall's arena continues to be a central feature'. Hundreds of £5 arena and gallery tickets are made available on the day for every concert. Admittedly you potentially have to stand during the concert, and queue for several hours if the concert is a popular one, but the having the option to turn up on the day and get a ticket for such a cheap price is quite special. Also, if you buy an arena or gallery season ticket for £190 it gets you into all 76 proms, which works out at just £2.50 per concert without needing to queue! If you really have to have a seat Circle tickets start at £7.50 for some concerts anyway.
Cinema Ticket: £5.50 - 9.50
Even the cheapest ticket at the Odeon cinema in Oxford (for a child at off-peak times) is more expensive than a Proms ticket, and the most expensive (for an adult at peak times) is nearly double the
Tesco Finest Parm Reggiano: £8/0.5kg
I don't know much about cheese, I guess this is pretty good cheese.
Kindle ebook: £9.99
Admittedly books, especially ebooks, vary enormously in price, so this is just an example to demonstrate that a good book by a popular author can quite easily be twice the price of a Proms ticket.
Abercrombie and Fitch boxers: £20
Yes, a pair of Abercrombie and Fitch boxers costs four times as much as a proms ticket.
1 litre of Tanqueray Gin: £25
This is good gin. Five times as much as a proms ticket though.