Obviously, a new name brand shortboard is out of your price range, so you're looking for a used board. If you want to learn on a shortboard, I'd recommend a modern fish type board. Look for something that has a relaxed rocker (between 4 and 5 inches... flatter is better) in the 6'2 range. Something like 12.5x19x14.5x2.5 would give you a bit more volume and stability, but you'd still be on a "shortboard" so to speak. Check out Al Merrick's Flyer shapes. That being said, if you're just learning, I'd say the learning curve would be steeper on a 7'6 hybrid, funshape, or big boy thruster. Be sure to stay away from thin, highly rockered, pulled nosed high performance shortboards.
go to a reputable shop, talk to one of the older guys. be honest about your skill level, don't be embarrassed and take in their suggestions.
I would want to learn on a board that can help me get up and stand, and learn on for a few seasons before plunking down 5-700 on a new board. Used boards are the way to go. Too many people give up and lose money on brand new boards. 300 will get you a good board.
Right now I'm riding a 6' 0" Lost round nose fish and i want to be a more aggressive board
That RNF sounds too big for you.... that + a pretty flat rocker doesn't lend itself to learning how to do snaps and such...
If your really concerned about learning to turns&snap and stuff, i would recommend getting a board with plenty of rocker... it will be slower, but it will just want to turn more.... when i was learning i found it much easier to figure out turns with a board that was well suited to doing them easily. Flatter boards are really fast, but I've found that they require a bit more finesse to be able to turn sharply.
i was on the chemistry site and i found a board that was used and is $150. Its a Chemistry 6'1 x 18 5/8 x 2 1/4 squash tail shaped by Jason Bennett. Do you think this board would be good for my size and skill level