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Sounds high to me but I know it's mostly labor charge. Both OEM hoses can be bought for ~$50, 3 gals of Toyota Pink for ~$70, and maybe another ~$10-20 for the clips. Max $150 for parts.
Are you handy? This is not a hard job if it's just the hoses. The bottom may be a bit tight but still doable. At this time, best to replace the thermostat and gasket (OEM only) if it's still on the original.
Inspect the vehicle yourself if possible. If not have her send you a picture or two of the hoses and definitely a second opinion. How many miles on the coolant? I'd take hose deterioration seriously if that's the case as it could damage the engine if they fail. If you're going to drop 600 on it, take it to Lexus.
It isn't hard to do, but is time consuming, and you do need to burp the system.
1) drain. 2) replace hoses (and probably thermostat while you are at it). 3) fill. 4) burp. 5) let the engine cool, top off the coolant res.
Is a hose leaking? how many miles? If you DIY, you will need some specific tools, the radiator hoses often stick to the metal and are a bear to remove.