I've got one, and I'm facing this dilemna as well.
Really, it depends on your goals.
There are naturally aspirated head packages from Gude that add 50 hp for about...like...$1500 I think. Pretty sure that's cost before installation too.
There are GReddy Turbo kits, as well. If you run stock internals, and stock boost on the kit, they add...I dunno, about 50 hp, but you can keep building that up, and strengthening the engine to handle more boost, but since the 92-95 Si's are SOHC, you can only take them so far. Figure on approx $2000 for the kit, then installation, and any kind of bottom end work you think you need to handle the boost levels you want to run.
I believe there is a Jackson Racing Supercharger as well that pushes 4-8 pounds of boost depending on the pulley you use. Adds oh...40-50+ horsepower, depending on the pulley. $2000+ You can't really go much farther than the bigger pulley with the supercharger, so this mod is sorta limited.
Then, there is the wonderful world of swaps. LS/VTEC, B16, B18, B20/VTEC, F20, F22, H22. Cheapo B16 swap? Maybe $1000 if you can find a cheap engine car or something to rip shit off of, and you can install it yourself, or with a friend. That can range all the way up to an H22 or Type R B18 with any number of turbo kits or N/A tuning options available.
If you want a quick 50 horses, I'd probably get the Gude package.
If you want to spend a bunch of money building up the engine, go ahead and get a turbo, and build that fucker. Either that, or find a GOOD engine shop, and have them do some crazy N/A tuning, and reprazent with your SOHC.
If you want a lot of options, and a lot of power potential, a swap is really your best bet. Choose the engine on your budget, and what you want to do.
Personally, I'm thinking about a B20/VTEC all-motor frankenstein auto-x'ing monster. Either that or a B18, since it'd be a simpler swap.