For 800 you can buy a decent entry level roadbike. Especially if you look for deals on last year's models (2013 models just came in september).

One thing you should not underestimate is bike fit. There is more to picking a bike than just looking at the component spec and picking a color. The bike has to fit your particular anatomy. It really is worthwhile to go to a bike shop (a decent one) get some advice and try out some different bikes. You may be able to buy something more high-end when you go secondhand, but the most important thing here is that you get a bike you are comfortable on and that feels good to you. I mean, if you have never had a road bike before, you probably do not even know what size frame you need.

One thing you will have to take into account is that you also need some budget for the basic necessities. Luckily you wont have to buy it all at once. Within the year, not taking into account gear for colder climates you would want a minipump or C02 pump, a floor pump with pressure-meter, a multitool, 2 spare tubes, tire levers, a jersey, a pair of bibs or shorts, helmet, shoes, gloves, degreaser/lube/basic maintenance tools, bottle cages, water bottles, glasses. These things will most likely cost you over 200 bucks together.