Most any analog computer headset should work on Echolink so long as it has an electret mic and dynamic earphones. Plug it in to your mic and earphone sockets, go to Echolink setup and your sound system should recognize it as an option. Just select it and you're good to go.
They are available most anywhere. I've even seen them in grocery and drug stores here in the US. More money buys sturdier construction but not much better performance. £5 to £15 is a good price range.
Allan - N4NLQ