i have come across most of the listed markers at some point or other, so i felt it right to comment.
JT 5.0 / 6.0
These are ok markers, i have seen only one of each ever down my local site, and the 5.0 was fine, but the 6.0 had serious build issues, and was returned. The talking grip simply isnt worth the money (i know there are other upgrades, but the point stands)
Infernos
These are good starter markers. The local site has just converted to them, some on CO2 some on air. They are a doddle to maintain, and quite relable. I have a friend who shoots a maxed out Inferno, and it is a accurate as most markers on the marker. And relable.
Spyders / Piranahs / Black Dragun
How can people force one above the other, the Piranah / Black Dragun are CLONEs of the spyder. Anything that the Piranah has, one of the many versions of the spyder will have too.
I personally think that the Clack dragun is a cheap imitation, and you get what you pay for in paintball
These were the old site markers. Again, easy to repair. but not as rugged as the inferno.
They are slightly more refined however. and slightly lighter.
Air / CO2
The only way on earth you will get air on a marker in that budget, is to buy a second hand marker, and but a PRESET air system. You can pick up preset 3000psi 1.1L (flat bottomed) airsystems for about £110 new. Maybe something second hand might come up though (check classifieds) But make sure that the bottle is HSE tested (NOT DOT) and is within its test date (3 yrs of previous test)
Co2 is a easy and cheap option. the marker will work on it, and you could upgrade when there is more money in the kitty. It is alot more incosistent that air in the winter, but thats a price you pay.
Hope that helps.
As far as exactly which marker, go out and try em out. (play a game or two if ya can) and work within your budget.
They are all entry level tourney capable markers, and Very capavble rec ball markers.
If you have any more questions, give us a shout.