Well this depends on your definition of "quick" and what your budget consists of. There are really 3 ways to go:
1) HCI: the standard N/A way to get power. New heads, cam and intake. With the right set of parts, you can easily see at least 100 hp bump in power. Will require a tune. Stock bottom end will be fine - though I'm not a NOX person so I don't know if a 100 shot on top of this will be okay. Used sparingly and at the right times I don't see it being a problem though. You will have to of course upgrade your fueling so things don't blow up. Just for HCI with awesome parts will run you about ~$2200 not counting labor to install (~$300 for cam, $1500 for heads, $400 for intake). On top of that, you will new injectors, new TB, new MAF, a tune, fuel pump and you'll probably want a new set of roller rockers as well. Probably another ~$1500 or so. You can knock down that price pretty good if you are able to source good, quality used versions of those parts.
2) FI: some form of supercharging. Turbo's are are an option as well, but even more expensive and more complicated. You can keep the stock HCI and just run boost. At around 6psi you'll get a little less than 100 hp. Supercharger kits run around $3000 to $4000 new. You might be able to source a good used good for a lot less. Quality turbo kits will run $4000 to $5000 if not more for all the supporting mods (intercooler, piping, etc.). You can run more than 6psi off a supercharger but you will need to think about intercooling at that point or perhaps meth injection. For a supercharger you will need to decide in the beginning how much boost you want to run. It's easier to crank more boost out of a turbo without going out of it's efficiency range - a supercharger typically has a narrow efficiency range than a turbo. So more planning required for a supercharger. There's also a little more flexibility with FI over pure engine - it's easier to get more power out of the engine assuming it can take it - just crank the boost. You will also need supporting fuel mods like option #1 - same mods for about $1500.
3) BOTH!!!!!! No really, you can combine FI with a better cam, better flowing heads, etc. Because you are using FI, you don't need the top of the line heads, cam, etc. Just something that flows better then the stock stuff. With this setup, 600hp is quite obtainable. This is of course the most expensive option. Probably ~$6000 at least for new stuff. At this point, you'll also be wanting a new, upgrading block with 4 bolt mains and the works.
The challenge is the target HP you are shooting for. If you wanted like 60 to 70 more hp over stock, you could get that fairly easily with cheap (as in "doesn't cost a lot," not "bad quality") HCI stuff like GT40 heads, intake, TFS cam or something like that.
It depends on what your limiting factor is. If it's budget, then I would be serious about picking a budget, and then try to maximize the power you can get for that, rather than starting with hp and then trying to make the budget fit. Because you will go over budget.
I hope this helps?
