Wired sensor bus technology
Seeing an atmega8 is &gt; 2€, your cost restriction is not that harsh., especially since you're also paying for the max485 (some 50 ct, I guess?). Also, your latency constraint/rate is very relaxed.
Drop the atmega, drop the max485, get one of the thousands of arm microcontrollers that come with CAN. Exactly that CAN was made for!
Distributor MCU product tables or octopart are your friends.