There is no such thing as 0% financing. Money has value over time, and a dollar now is worth more (at todays rate about 1.03) in a year, and with compounding it does begin to add up. The Present Worth (cash option price) for 20000 in 5 years @ 3% interest is about 17,250. Kubota knows what the present worth value is when they sell it, and they just compute the price based upon intest factors and term.
For me, it didn't matter. I didn't have 17k to offer in cash. But in fairness, I accepted the cost to have the machine. Everybody in the manufacturing chain has to make money for the system to work. My salesman was an old friend. I make enough money to afford the tractor. Even though I could have negotiated hard, I would have been reducing his (and the dealer's) return on investment. I bought it locally because I want that relationship to be healthy, and I know that at some time, I will need their help and business. Supporting local business is important, and the bottom line was that I was satisfied with the deal and the overall experience.