I concur with the others; The radiator was close to 20 years old, that’s a reasonable life expectancy. There’s likely nothing you could’ve done to make it last any longer than it did. Given the age of the vehicle, I probably would’ve had the hoses replaced, radiator cap, as well as the the thermostat. The $520 price is perfectly reasonable, though I don’t think OEM coolant would be a huge deal for this vehicle, probably could’ve saved $20 or so going with an aftermarket brand.
Keep an eye on the coolant level over the next few weeks. You’re probably okay, but if the coolant level starts dropping inexplicably, you might have a head gasket failure, this can be confirmed by either the engine oil level increasing (coolant makes it into the oil pan), or by a signifcant amount of white smoke coming from the exhaust (coolant makes into the combustion chamber and/or exhaust system and is vaporized by the heat).