I have used both kubota filters and wix. They both work fine but the price is not much different The biggest savings can come from your fluid. Tractor supply sells their premium udt that meets kubota, deere, new holland specs. You can get 5 gallons for $39. Neither deere nore kubota makes their own oil and as long as meets the warranty specs you will be fine. I have used their fluid in my 2 kubotas, massey and new holland tractors for the last 6 years with 0 problems.
I believe Ashland does Kubota fluids/lubricants.