All the differently branded "303" fluids are essentially the same and not beneficial for your Kubota.
Stay with at least a UDT equivalent (SuperUDT for newer machines). I use Chevron THF1000 with good luck but any direct cross-referenced brand should work. Avoid those fluids that claim compatability by listing machine brands instead of specific fluid listings.
Gurn, you might want to check with a local fuel supplier. Where I get my fuel also handles bulk oil. I bought a drum of trans/hyd fluid from my fuel guy for a little under $7 per gallon. I thought that was a good price for cheap oil.