The advantage of the "drop-bar" typical on road bikes is a variety of hand positions for comfort and different situations. You also have numerous places to adjust the fit of the bike, and different manufacturers have slightly different frame geometries that can make a big difference. +1 on the suggestions to try a lot of bikes and figure out what you want and what fits comfortably.
Something else to look at are the so-called "fitness bikes" or "performance hybrids". They are basically road bike style frame with a mix of road-style and some less-expensive (larger sales volume) MTB components and a flat handlebar. Some of them (Jamis Coda line) also come with drop bars or could be retrofitted ($$) later. In my experience, these bikes seem to be more forgiving of fit than a road bike, will give you a nice ride, and may be a good compromise between performance and cost for you. Some bike shops are starting their end of season sales, so you may be able to find something on close-out.
Craigslist is certainly an option - my son's bike (Jamis Coda- that's how I found out about them) was a Craigslist buy. If you can, bring someone who knows bike with you - they can spot the problems that look bad but are easy to fix, and the ones that are expensive. In my experience, good bikes reasonably priced will go quickly.
Good luck!