Have you visited the 911 chips dyno section? They have several different engine configurations, and although not all the information is given sometimes, you can get a pretty good idea of what might be a typical result with such mods as what you are thinking.
911Chips - Porsche Dyno Runs
As far as cost, if you use a combination of Pelican parts website, Wayne rebuild book, Bruce Anderson's book, and Ollie's machine shop website, you can get a good idea on cost too.
Home Page
I would be inclined to stay with your current P&Cs, single plug, get a good machine job on the engine, get a good set of bearings from Steve Weiner or Henry Schmidt, recondition rods with ARP bolts, DC19 or WEb 20/21 cams, and custom chip, and I think you'll be close at least in corrected crank HP. Then if you're not quite there, remove weight to get to you performance target. Should be do-able.
If you go ITB's or carbs, it's another order of magnitude more expensive to really get you're money's worth. Just my noob opinion.