A tune up is mainly just a routine change of spark plugs and wires. The car runs better afterwards.
For 500 bucks the car should last at least 6 months. My equation is for every 1000$ you spend, you get a year out of the car plus planned and unplanned maintenance. A car with nearly 200k miles...
That is way too general. Are you looking for something in the price range of $1,000-$2,000, $3,000-$5,000, or $6,000-$10,000?
Need more info before one can answer this question accurately.