If you don't already own them, you'll need to take at least the loader and air system into account straight off the bat. Once you've taken a chunk out of that budget for these items you'll have a better idea on what you have available for the marker and you can get the best you can afford.
As to what is the 'best' no one can tell you that. Most decent guns from the last 5 years all so all get the job done very well, they almost all shoot the standard 10.5 balls per second that's common now. Beside cost your decision will come down to ergonomics (some guns feel better in the hand that others), maintenance and reliability, appearance and what sort of gun those around you use.
This final point is quite important as in my experience it's very useful to own a similar marker to the people you play with. When I started playing, almost everyone around me used Angels and although they were expensive it was common sense as everyone had spares, there were techs everywhere and there was always someone around to borrow x or y part/tool off. These days I shoot an older ego, as do most of the guys I play alongside, this makes things simple if any of us have a problem.
What sort of paintball are you planning to play? Scenario games, walk-ons, or tournaments?
