What is the max current consumption on bus side of isolated RS485?
Yes you are right. Thats what the datasheet states: 58mA at 20Mbps.
You may be interested, I think it was LT (linear technology), today part of analog devices, used to offer (&gt;10 years ago) a part which integrates a RS485 transceiver + a dc/dc switchmode converter... so you only need a small transformer and you have a fully isolated solution with 1 IC. Maybe Ti is offering something similar.
Last maybe: Maybe you find these products with searching the keyword profibus, a very common RS485 based industrial bus.

small correction:
https://www.analog.com/media/en/news-marketing-collateral/solutions-bulletins-brochures/5745225673953RS_485_2006_c.pdf
here you find what I mentioned, but it's a 2 IC solution... you also need a small LDO.