What is estimated scrap value of 1999 Subaru Legacy Sedan?

Scrap value is according to weight.

No tires wanted.

No battery wanted.

I'd replace the thermostat and top up the antifreeze first before getting rid of the car.

I wouldn't give you $100 for a 22 year old car with a blown head gasket.

Between $150 and  $300 at a scrap yard.

$200.  You can try replacing the thermostat.  No luck,get a pressure tester and check for coolant leaks first.  Could just be a bad radiator.  Not an expensive fix.

Scrap value is the same on all vehicles, between $300 and $500, not depending on condition but on what area of the country you live in and what the market value of any car sold for scrap there is. If you want more than that standard scrap value for any and all cars, then you either have to not sell it as scrap to a scrap yard but to a private party or you basically have to go into the scrap business and scrap it by selling off individual parts of the car yourself until you get out of it whatever you want to get out of it plus what it's going to then cost you to have to then pay a scrapyard to go to the trouble of coming and hauling what's left of it away for you.