This Auto transfer switch (TOMZN ELETRIC TOQ3-63/4P AC-33IB Transfer Switch) I found on Ebay for 50€. It consists of two 4P-breakers coupled with a motor driven mechanic. You will find similar designs also on Amazon. It is not as high quality as ABB or similar but affordable.
Bay the way, for my 60kW-PV i need to have 200A automatic breaker for the grid and plant protection. And the auxiliary relay of the 2k€ ABB breaker make a lot of trouble.
I use the ATS to bypass the MultiPlus II for service times the could be a manual transfer switch also fine. But i want to test the ATS if it is also worth it for grid fail management.
Now after one year operation the switch 50€ is doing its job, ~10-30 switches.