http://www.sftmx5parts.co.uk/

Meant for an mx5 so not sure if the wiring might need a bodge, but at £30 they look like a better deal than a honda S2000 starter. (accessories section)

Any toggle sitch for ignition and any momentry action switch for Start will do the same job just make sure there both up to the current. I'm sure RSwww.com or MaplinUK you could get the bare components for less than 15 Quid. You could also put in a Light to show ignition.