to be honest, there are hardly any cheap tuning modifications for NA cars that are worth doing (i.e. noticable improvements), unless your going to do the lot and get a healthy HP increase.
All the routes to big power involve new engine managemt and/or a turbo conversion.
of course, if your handy with a dremel, and dont need your car for a few days, you could always port and polish your head and manifold. Depending on the job you do you could release upto about 15, maybe 20 hp.
You'd be wasting your money as well if you get your car remapped before you get any mods done, as it'll need re-mapping again as soon as you improve another aspect of the engine.