My local shop in Chiangmai has it fairly cheap, but it's 3 hours away. There are a couple of other online sources (Lazada and lemontree) but they're ridiculous prices... 

 

It's the same as what's often given to horses for animal feed (though sometimes fortified as well). 

 

Anyone know of a reasonably priced source to buy from that can ship?

Finding a reasonably priced source, in Thailand not easy as it will be bran from imported wheat.

You need to find a mill that mills wheat, as most wheat comes into Bangkok, I would say the mills will be in that area, a fair way from you.

Wheat bran feed to horses, a friend of mine had some horses he uses to feed them rice bran, from our local rice mill.