Spending 50k on a non vtec motor for 30whp isn't enough. NA gains are expensive, that too on a small displacement motor, that too a sohc! Adding high compression aftermarket pistons, good cams, springs and retainers, gutted intake manifold, a reasonable port job, proper intake, velocity stack, bigger throttle body, injectors, fuel pump, headers, chipped ecu etc are going to cost you alot. Better go turbo, your engine will hold around 170whp safely (provided that it's current health is optimum). Or, save up and spend wisely once.
NA build for 150ish+ whp won't cost you below 200k. Even if you budget it out wisely on parts, labour, tuning etc. Better save that money and go turbo.
I've got a fully built D15 turbo charade in my collection, has all built internals and tuned it myself. Would be over 450whp roughly since i didn't hit a dyno yet. D series has alot of potential if you act wisely and pick the right route. I'm working on my other cars these days, once i get back to this D series, I'll be going AWD and over 550whp.