2009 Toyota, What are typical cost to replace O-rings on the Rack & Pinion unit

Typically the complete rack assembly replacement is required as the o-rings or seals inside failed for the very same reason the replacements will fail..!

Toyota steering gears seem to leak more than other manufacturer's gears in my experience. As Pushrod said, replacing the gear is the only repair process to repair this. And if the leakage is nominal -- i'd probably just top off and monitor. Watch the "bellows boots" -- the rubber boots on each end of the gear -- where the fluid typically fills and swells the rubber -- if they get to be bulging with fluid, the time will be sooner than later to replace the gear. And yes, this repair is typically pretty expensive unfortunately.