I have the same problem with coolant leaking internally. If you have recently change the water pump, thermostat, radiator, and radiator cap, then it is more likely the head gasket. Several auto repair shops estimated the job to be between $1200-$1500. What you need to ask them is for the price of the head gasket set and labor. You can save a lot of money by buying your own head gasket online or at the autoparts store. I got my head gasket set for $100 and the repair shop quoted me $300. Also, use your bargaining power on labor but don't do it on Friday or Saturday.
Monday is best because that is when their business is usually slow.
Total cost for the Head Gasket repair for 1992 Lexus ES300.
$100 Head Gasket Set
$400 Labor
$150 Machine Shop for the Valves (Optional but recommended)
