I'm buying an 08 Prius hatchback from a friend (with 36,000 miles). He's had the gas gauge problem for a few years, ever since Toyota had to correct a big electrical problem. I wasn't comfortable with having to fill up every 200 miles so we brought to the Plymouth MA dealer to see if they could fix it before I bought it. They did in about an hour. They said the fuel gauge just needed recalibration. NO CHARGE.
That's good. Even if the gauge was not fixed, there is no reason that you would have to refuel at 200 mile intervals. Use the MFD mpg and miles traveled gauges to determine fuel consumption, and reset both when you refuel.