I've seen A LOT of posts about making HP with a 318-So why is it so ???

If you’re doing a true minimalist bucks down “freshen up” type job...... how far you’ll have to go, and what it’ll cost is mostly dependent on the condition of the core engine you’re starting with.
If the crank finish and sizing is decent, and the bores don’t have any type of “damage”, you can get out of it pretty cheap if you’re doing most of the labor yourself.

In the 80’s when I was doing a fair number of these types of jobs, I’d always spend a few dollars at the machine shop having everything cleaned.
Hot tank the block and rotating assy, all the tin and covers.
Polish the crank, dingleberry hone bores, cam bearings, freeze plugs, dist bushing.
This way you’re starting out with something nice and clean.
The heads usually needed ex guides, and I’d have the seats done and decks cut, valves bead blasted and refaced.

Re-ring kit, cam and lifters, timing set, and usually valve springs if it wasn’t getting a stock cam.

Keep in mind....... the engines were 35 years newer than they are now.