Tokyo Marui are the most common starter AEGs but Star have made a couple of guns in the same price range (in addition to their other, more expensive models).
The Tokyo Marui FAMAS is pretty much the cheapest gun you can get that is suitable for skirmishing. It's $182 from Redwolf Airsoft, though I'm sure you can find a second hand one for less. Remember though, you'll need a battery, a charger, a face mask, and at least one hi-capacity magazine. You're probably looking at another $100 on top of the price of the gun.