Well, having had a quick look on VGI, the Saturn version definitely looks like the cheapest. Sealed copy there for £40, cheaper than a 2nd hand PS1 version.
£120 for the PCE version with a cutout from the magazine ..
Feeling quite glad to be Sega fanboy at the moment. Hopefully a bit more searching will find me a decent non-sealed copy for a bit less than £40 ...