3 ideas
Start with take-home pay. Subtract every cost the job forces on you: commuting, work clothes, job-related meals, decompression spending, and job-caused illness. Divide the result by all the hours the job consumes, including commute, preparation, and recovery time as well as paid hours. The result is often far below the nominal hourly rate, and it is the true exchange rate between your time and your money.
Money is treated as 'life energy': the hours of your finite life you traded to get it. Dividing any price by your real hourly wage turns the purchase into hours of life spent. You then ask whether the item delivers fulfillment in proportion to those hours, which makes spending decisions concrete rather than abstract.
Fulfillment rises with spending as survival needs, then comforts, are met. It peaks at a point called 'enough', and past that point it declines, because more possessions and spending bring maintenance, clutter, and the work hours needed to pay for them. By tracking each spending category against the fulfillment it actually produced, you find where you have passed the peak and can cut there without loss.