The Elacin ER20 is a cost effective, ready to use, one-size-fits-all earplug that closely replicates the ear’s natural frequency response. The earplugs reduce sound levels by 16dB while minimizing high frequency roll-off providing high fidelity hearing protection for musicians and users in clubs and concert arenas. They can be reused.
Cheapest price I could see online was £7, but more typically they go for about a tenner. Comes with a carrying case and optional neckband.
Bought a couple of pairs (always lose one of a pair...) at HMV in Westfield, London. Plenty on display at the back of the store.