I have found that one can never predict future car repairs - doesn't matter if it is a new or old car - high miles, low miles, or no miles! There is a certain standard of maintenance that should be adhered to, and expected. Brakes, tires, oil changes, trans services, alignments, wheel balance, etc are always on you and should be expected. Then comes that unexpected repairs, which could be absolutely anything and unpredictable. Question is who is going to pay for it. Sounds like you want a warranty that will take you out to 300K miles!

New cars have warranties.
Newer cars have extended warranties.
Anything over 10 years old (or high miles) will charge you for a warranty but will only pay up to the value of the vehicle. So much for the $10,000 engine repair they advertise.

None of these apply to your old, high mileage Blazer. Given that you cannot predict what will happen in the next 150K miles you will either have to fix problems that occur yourself, or pay someone else to do it for you. Some people get lucky and have few problems. Others do not.

Best wishes

 

To help prepare you for what could be ahead, here is a list of my Blazer costs (last 10 years). I'm guessing maybe $400/year parts for recently but i'm increasingly losing DIY interest so maybe a better future number is $1200/yr. and let the shop do it. Still not high enough yet to justify a replacement, especially with a used car, with unknown history and who knows what repairs coming up.

The early Tesla model 3's are coming out of battery warranty starting this year (= cheap) so maybe I'd consider one of those for driving in the city. At 15 cents a kwh, a 300 mile fill up cost $11 and they are a crazy fun experience in acceleration.