Cylinder head, cam, and intake swapping is probably the most affordable method. For around $2000, an HCI package on an otherwise stock engine should produce a respectable 350 horsepower. You still require matching mass air meters, throttle bodies, and fuel injectors (24 or 30#). If you have an SN95, it might be worthwhile to upgrade to an 89-93 ECU and MAF or to consider getting a custom tune or even both.