I flew a piper warrior for a number of years which is a 4 passenger fixed wing with a 160 HP engine that cruised at 120 mph. And while i used full power to take off and climb, i could reach 120 mph with maybe 60 percent throttle. You don't need a lot of power to stay up in the air and cruise its just that since the speed limit below 10,000 feet is 290 mph and above 10,000 feet Mach 0.999999 aircraft designers frequently put more HP behind their aircraft to hit higher speeds. If you are traveling 200 mph of course you will burn more energy then traveling at 80 in your car by a wide margin, but for a lot of people the difference in energy is well worth increased speed.
The real reason why no one flies in general aviation is everything is so expensive to purchase and maintain. Brand new starter aircraft are $200k, insurance is $3k-$8k a year depending on experience level and just the overhaul interval on the ICE power plant equates to $10 per flight hour (2000 hour TBO for ~$20k cost). Avgas or Jet A is a big expense line but when you go and rent an aircraft at an FBO fuel equates to maybe 40 percent of the cost of use while insurance, storage and maintenance costs take up the difference.
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