ive just rebuilt a e31 head and had it shaved, ive allready got a exhuast and k&n's, the stock exhuast manifold looks like it flows pretty good so i dont know if a header if worth getting, oh yea i forgot im running a 60 ish shot of n2o....

A header and a good free flowing exhaust system would be one of the best mods to do to use what you have the most effectively. Going to cost more than 200 bucks, but will give you the most perforamance gain at the lowest cost. Especially if you use the Nitrous, you'll need to get the exhaust out or the shot of Nitrous is going to cause you problems.

If you are running a stock ignition, that would be the first place to spend your money, as with nitrous you'll need the best spark possible to keep it from detonating. If you use a higher hp shot of nitrous, you'll need to upgrade the fuel system to supply more fuel to go with the nitrous. at 60 the stock should be OK, but be watching for lean conditions by keeping an eye on your plugs and be carful you don't get spark knock. Both can be fatal to pistons.

im running a wet shot so fuel shouldent be a problem, but ignition would be a good mod

When all else fails go with cubic inches. You could get an L28 engine block from a junk yard and bolt that to your head and get some more HP. If you get one in good condition it could be less than $200 but with any change the little things can exceed you budget quickly.

To stay with your current compression ratio go with an N42 block ('75 280Z - '79 280ZX) or for an increase in compression go with a non-Turbo F54 block ('80 - '83 280ZX).

The engine block model number is stamped on the block near the motor mount under the exhaust manifold.

Of course the extra cubes would like a bit more fuel.

you should save that money for the speeding ticket. Sounds like you're already burning rubber.