margarinal returns 

"Bare-bones" proceeds/rewards that are of far less value/usefulness than whatever it was that you originally invested into said venture... in other words, it's like you put fresh pure premium dairy-butter into da mix, and only got stale margarine back out for all your sweat 'n' toil.

I diligently updated my profile and paid my dues to a local dating-service in the hopes of scoring some sweet fresh "milk", but all I got was a bony plain-Jane past-middle-aged biddy wif A-cups and a hairy snatch dat smelled funny --- talk about margarinal returns!

margarinal returns by QuacksO November 17, 2018

diminishing marginal returns 

phenomenon in which greater input of effort, money, etc. yields smaller results. Crucial part of the idea is that if you're using x to get y results (where y is the thing you want). then additional input a will yield additional results b, but not in the same proportion as before.

On average, before, you put in x to get y, so your yield was y/x. But if you increase x by amount a, then your results will be y + b, where

(y + b)/(x + a) < y/x

and this will only get worse.

Diminishing marginal returns (DMR) is used to explain why the supply curve in economics slopes upward, i.e., increasing the quantity supplied requires an increased price of most things.

Sometimes DMR is more than offset by "economies of scale," which allows more of a thing to be supplied more cheaply than a small amount.

At first his flowers and treats swept her off her feet, but then he had to do more and more lavish things to please her. It was a classic case of diminishing marginal returns.

diminishing marginal returns by Abu Yahya June 3, 2009