Found someone selling a used WD100EFAX for £87, that's £8.70 per terabyte which is pretty good in the UK but no warranty obviously.
Actually the seller has a pic of a white label WD101EFAX but says WD100EFAX in the description and they haven't answered whether the pic is the actual drive yet, but they're both basically the same apart from the 101 being air filled and the 100 being helium filled.
I've read up on the drive and it seems kinda old and from the time period where WD wasn't being honest about their specifications?
I don't really need it but I guess I could just use it as a third backup drive and then put it in an array later on when I've got one. Otherwise it just seems like an extra drive for no reason that could fail within a couple months and become an expensive paperweight.