$800,000 sounds about right for a new top of the range farm machinery (not sure about a tractor though?) and with no alternatives, will continue to be run to be run on fossil fuels for the foreseeable future. Farmers depend on these machines for the income and need reliable machines that can work - sometimes - 18 hour plus days. Would be hard to get an electric alternative for that. Perhaps fuel cell tech would be more suitable for agri/hort use?
I don't think it will be until the 2030's that we start to see any real movement with the likes of tractors and even then, it's pretty normal for farmers to have tractors that are decades old still in service. However, John Deere is already developing electric tractors so we will probably start seeing some options in the next few years. I don't think we're likely to see hydrogen make any inroads for the likes of tractors, markets for hydrogen keep dropping the tech.