Swap in a 3.3 litre flat 6 from an SVX (Between $2,000-$4,000). Instant 230hp and 228lb ft of torque Naturally Aspirated. Add a custom equal length header set (Made at your local Exhaust Shop that specializes in mandrell bending). Then add a Catco Hi Flow Cat and custom midpipe with a Brullen muffler section. Throw an intake on there and you should be running 250+ hp Naturally Aspirated.
Later on down the road you could buy a TEC-II (Engine Computer) and custom 7-9psi turbo system. At this point you will definitely be putting up horsepower numbers closer to the 320 range (at the crank). Of course in the mean time you are going to have to replace your tranny and driveline to handle that much torque.
Honestly the easiest/cheapes way for you to acheive 200+ horspower would be to run a 50 shot of nitrous.