If I were you I'd go to
UCoat It America - Garage and Concrete Floor Coatings
You'll be extremely happy with the finished product and I think you'll be about right on budget. The U Coat It system is hands down the best looking epoxy floor coating I have seen. I will be using it in my detatched garage.
I used the Rustoleum stuff from Home Depot almost 3 years ago on my main garage and it is holding up great, however it's not half as nice looking as U Coat It. Of course I coated a 24 X 30 garage for $200 including supplies. I was very particular about the preperation process and I believe that is why the cheap stuff is still sticking. Here's what I did:
Since this is a new house, DO NOT park your leaky car in the garage and stain the floor.
Buy a stiff bristled brush that you can mount to a handle, buy a handle mounted squeegie, a gallon of Muriatic acid, a big bag of Baking Soda, and a metal pail with a sprinkler spout like for watering plants.
Sweep the floor.
Hose the floor down good. Remove all loose debris.
Squeegie the floor to get it pretty dry.
Use a respirator if possible and pour the acid into the sprinkler pail.
Use the pail to spread the acid over the entire floor.
Spread it around with the brush.
Wait 10 minutes and rinse it down.
Spread baking soda over the floor to get the ph level back to normal.
Use the brush to spread it good.
Rinse the floor and squeegie to dry and repeat a second time to make sure you get the floor good and clean.
Let it dry overnight and start spreading the epoxy the next morning.
Make sure to read the instructions as to the correct temperature range for spreading the epoxy.