The Kubota spin-on filters are reasonably priced, IMO, and are a good value for their quality.
I use “cheap” filters on some equipment (such as my Sear lawn tractor with a B&S engine...the Sears or B&S filters are priced at $11-$16 and the SuperTech/Purolator/Motorcraft versions are all less than $4 at WalMart.).
I don’t think you’re going to save a bunch of money over the life of your tractor using aftermarket filters instead of the genuine Kubota products.
The hydraulic filters operate at very high pressures and a cheap aftermarket product in that location is not a good idea, IMO.