There's one place that does organic hay, which is what the goblins arrived with, and they loved that - but it was organic, with the price tag to match, and that as in January. I dread to think what price it is now, it was horrendously expensive even then. The Happy Hay stuff has always been good though, I'm yet to have a bad box that I can remember. Cam chooses to nest in it occasionally (mate, WHY?!), I'm not sure what I'll do if they suddenly refuse to eat it.
Used to be easier when I could grab a bag of Burgess, but it's been years since I've had a bag that didn't immediately need tossed out. Comet and Blitzen would eat any hay you put in front of them, so at that point I could get away with Nature's Own, but the goblins just like to be awkward like that.
I'll pay £16 for 5kg, hell I'd pay more if I needed to, but I can't imagine the stress of trying to work out what hay they'd eat, if not for the goblins turning up with hay they went mad for I wouldn't have known either.