Good news! I will buy Fair SaaS (1ws + 3nodes, with year subscription, when it will be availiable), and will be able to buy when needed additional Fair SaaS (1ws + 5nodes) for my render-farm, if there will be commercial work or long personal renders.
So for my 10 PCs it will be 25 EURO per month (300 EURO per year), and additional 30 EURO per month, for a few months, if I have work with "full load", and with ability to cancel this additional subscription any time.
I am happy now :)