Bikesdirect Motobecane Mirage SL $450 STI 700c road bike

Bikedirect bikes.  Loved and hated.

The Mirage SL is the cheapest road bike I would consider from bikesdirect. If you live in an area that has a good used bike marketplace, you can likely find a better quality, barely used bike.  Good brands to look for are trek, giant, specialized, trek.  Search craiglist from $250-500.  Post up what you find on https://www.reddit.com/r/whichbike/ and bike nerds will give you advice,

If you like somewhere with a poor used bike market, the $450 mirage SL might be your best option for a road bike under $500.
http://www.bikesdirect.com/products/motobecane/road_bikes/mirage_sl.htm

This is a bike shop quality bike.  From the aluminum frame, to carbon fork, to beefy wheels with cassette hubs. Shimano Claris STI shifters with 2X8 , to FSA compact 50X34 cranks, this is a current, decent quality road bike.  It compares favorably to bike shop bikes costing $700-800.  For example the $770 Trek 1.1

Sure, the tires, bars, and seatpost are a bit nicer on the Trek, but those are things you might change anyways.

One big advantage of the bike shop bike, is that it is assembled and adjusted by someone who knows how to work on bikes, and uses proper lubes.  This makes a huge difference!  If you bring your BD mirage SL to a bike shop, to have them put it together and adjust it, expect to pay $50-75 labor, and it's worth it!  If you are mechanically inclined, and willing to invest $25 or so in tools and lube, and willing to do a little research, you can do it yourself.  Mostly putting on the front wheels, pedals, handlebars, seat as far as assembly goes, pretty easy.  Adjusting the gears, and brakes, and truing the wheels is a bit trickier.  You will need: good bike chain lube, like triflow or prolink, grease, car bearing grease or white lithium is fine.  Metric allen keys.  Cable cutters.  Eventually, you'd want a chain tool.

Unlike other budget options, like department store bikes, this bike comes in many size options, so you can get a bike that fits you if you are tall or small.

The main cruddy thing for a commuter on the motobecane, are the poor tires.  They get flats easily.  Two of the more popular, fast, flat resistant commuter road bike tires are the continental gatorskins, and the Panaracer Paselas.  Gatorskins start at $40, Paselas for $30 for the PT puncture resistant ones.
This bike can fit up to 28c wide tires, 23c would be super skinny, 25c in the middle.  Fatter tires will be more comfy, and less prone to flats, if slightly slower.  Most commuters run 28c or fatter.

Other wise, it is a good bike, and should wake up call to people that try to sell 90's STI roadbikes that aren't particularly fancy or special for more than $400.

One thing about this bike, and road race style bikes in general, is that is has low profile brakes, that make it tougher to fit fenders, or mud guards.  And make it so you have to run skinnier tires, 28c max.  And 25c if you want to run fenders.   Hybrid, touring, or cyclocross bikes let run have fatter tires and fenders.

This bike is good for someone that wants to get into roadriding, or needs a very fast, efficient commuter for long distances, and is willing to give up some comfort.  The best upgrade you can do to this bike is new tires.