If I were a newbie with your budget, I would probably get the Tippmann '98. It's a very low maintenance gun, and as such, not all that modifiable. Get yourself an aftermarket barrel and you're all set.
If you're looking to "trick out" your marker, then maybe go with a Spyder, like I did. They have lots of aftermarket parts available--some useful, some not. I've added a regulator to mine, a drop forward, macro line, SS barrel, Venturi bolt, .45 frame w/ Hogue wraparound grip, double trigger, etc. All I need is a turbo valve, and I think I'll be done.
Now, if I were a rich man, I would probably get an Angel. Then again, my friend has the AutoMag R/T, and it's a nice gun as well.
This sure is an expensive hobby...