I was actually going to suggest this (sort of) option on your previous thread.

Most so-called 'fixies' are going to come with a rear wheel that enables you to set up for riding fixed (you must always pedal, no coasting) or a freewheel (which will ride like a normal bike, with coasting, just one gear.) Fixed gear is super fun on flatter terrain, whereas single speed is a bit easier especially if you have rolling or hilly terrain.

It should be possible to get a fairly decent used single speed bike in your price range. They often do not come with drop bars, but it's really easy to install new bars and brake levers. Even if the bike isn't the latest and greatest, it will be lighter than any low-budget road bike, since it does not have the heavier derailleurs, cogs, and so on, and will let you ride in a more aggressive position. If you want a new bike, check Bikes Direct.

I've been riding fixed and/or freewheel single speed bikes on the road for a good number of years - at first because I couldn't afford a nice road bike, now because it's a nice change. Doing hills on a single speed will make you strong, and downhills can still be reasonably fast if you work on cadence and aerodynamics.