$600 overall, hmmm. Good call on Tippmann by the way, their really best for rentals and not much else due to performance. I'm going to read this thread and write things as I see them.
First, Dangerous Power makes a decent spool valved marker, but I had trouble with my G3 way to often to trust. And both my G3 and G4 froze up in the cold temperatures, forcing me to sell them.
Second, Smart Parts turned to GOG, and I do like their GOG G1 and Envy. At your price, I'd recommend them. My Vibe (previous version of the Envy) is a sweet marker, and doesn't chop paint in the least. Shoots smooth, and efficiency is ok. The company itself and its policies are... not so hot though.
Third, everything MaxFactor said except the Axe I agree with. He nailed the shot distance argument perfectly.
Fourth, Tiberius are really for those that like to sit and "snipe" from a distance. Its a playing style that isn't for everyone.
Fifth, Azodins are like a Tippmann, except stacked tube blow back (think Spyder without the leaks). Entry level, huge bang, and fun to run around with but not really the best option.
Sixth, I agree with Max again on the sights, paintball guns are not accurate enough to need one and with a mask its way to hard; Riser or no riser. However, the G1 has a convertible feedneck, so you could offset it to the left or right for a sight if desired.
Blackheart, Max nailed it again. :thumbup: Though you'll have to ensure the eye's are clean.
As far as my opinion, I'm staying out of the marker recommendations, but will say this. Don't skimp on the gear (which you probably know).
Your mask will make or break your day, it must have thermal lenses and comfortable. If you have to drive an hour to a store, DO IT so you can try some on. Then price check before buying.
Your tank should be HPA for a decent marker. For scenarios, get a full size like the 68/4500, and a cover to help protect your $130 plus tank.
Get a comfortable pod pack and several pods, depending on how much paint you put out. At my favorite field, it sucks running half a mile to the set up area.
Get a electronic hopper, a gravity is a misery machine. The Invert Too is great for $50.
Sore knees? Elbows? Get pads.
Barrel, depending on the temperature, your local paint will tend to be very large or very small. Buy a barrel that fits better than the standard stock .690's. Research overbore / underbore on your own time if you really get into it again.
Expect for this to come over $300 right here, leaving about $250 for your marker. It's a lot, but I screwed around with 40 to 50 markers before I realized that the marker was the last thing I should focus on. Enjoy!