You wonder if it'll go to 500,000 miles or kilometers 500,000 mi no problem almost every Toyota I've driven since I don't know say 1974 Corolla SR5 all went 400 plus thousand miles and one even without an oil change no kidding.
Now if you leave it out in the Texas baking heat all the time like in the middle of nowhere in the Sun that's not going to fare well on the paint and body molding and interior trim but the car will easily run to this mileage the 300 you're asking about and even the upper 400s without much of any work just tires and main consumables no excuse for it not to make it actually unless you're just beating the car to death.
There are older threads around here about the early Gen 2 combo meters that stop at 299999. If I remember right, there might have been a solution involving a later-year Gen 2 combo meter and having it programmed to match your current mileage. Don't bet too much on my memory on that, but those old threads are around.
Nothing wrong with your memory. Texas Hybrid Batteries shows a "300k upgrade kit" for early Gen2. A later 2006+ CM plus installation parts. Posted via the PriusChat mobile app.
