I bought a couple of TB6600 drivers from Aliexpress (Amy Supermarket was the supplier, although my specific devices don't seem to be listed any more). I've used these off 24V driving NEMA17 motors without any problems, although I haven't worked them that hard. I see that similar devices are available via Aliexpress at £5-£7 or so with free shipping, or go for Lucan07's version via eBay. Trouble seems to be that they all look more or less the same, but you don't know what's actually in them, I guess.