KNEX cobra's coil roller coaster just £14 at John Lewis. £20+ elsewhere.
There is a £2 charge for click and collect unless you spend £30. There are other toys on sale at mo. There is also the KNEX Ferris wheel which is £15. You can get Ferris wheel on Amazon and Smyths for £15 too but currently retailing at £35 at the Entertainer, Toys R Us and Debenhams so still very good price.
Don't know why the link isn't working. Try this...https://m.johnlewis.com/k'nex-cobra's-coil-roller-coaster-building-set/p/2771337