A built in harness is a mixed blessing. My old HL jacket has that--but once I got an inflatable PFD with (a better) harness, that became baggage which mainly sits in the closet.
Good recreational foul weather gear (Marmot, REI, etc.) is going to compete with the best marine gear. Cheap $35 plastic rain suits, will always be cheap $35 plastic rain suits. They serve a purpose even if it is a limited one.
I'd have to agree on the construction details being a big part of the expense, as is durability. Heck, even GoreTex comes in at least 3 grades with varying warranties, if it isn't fully seam sealed with the "Extreme Wet Weather" tag on it, you can still get wet in it. And if you are in situations where you will be sitting or kneeling in water--it's going to come through any breathable fabric at that point.
But I got started with cheap raingear and it served a purpose, it was better than nothing. Then one day after some storms, my friend and I were sitting in a deli letting our laundry dry, ignoring the really funny huge puddle forming around us, and I decided "cold + wet = miserable" and went after some real foul wx gear. But, until and unless you are making that expensive committment to sailing....the cheap stuff will often have to do.