Used Cannondale F500
How about a bright red Cannondale mountain bike?
This was a cool mountain bike fifteen years ago. It was light (still is, actually) and pretty comfortable with the headshock suspension fork. This F500 is from the middle of the line, so it’s outfitted with Shimano Deore LX components and Sachs twist shifters.
Put slick tires on it and ride on the street, or take it as it is and head for the woods. All yours for $349.
This is a medium frame size, so it should work out pretty well for a rider between 5’5″ and 5’8″ tall.