New coil
 

So I have decided to replace my coil as it is getting more and more susceptible to not starting/cutting out when wet and it is also more than a decade old. I found this cheap one on ebay;

http://www.ebay.co.uk/itm/Yamaha-XT6...gAAOSwa~BYPe0G

Are these cheap ones as good as OEM or is it better to pay almost 5 times more for the OEM coil?

For that price it's certainly worth a punt. I wouldn't expect to get as long a life span out of it as you have the original unit.