Sometimes there are things, even expensive things, that can save you a bundle. Maybe it is the fancy coffee maker that helps you break the Starbucks habit, or maybe it is a Netflix membership that cuts your entertainment costs to nearly nothing. For me, it is my Soda Club carbonator.
I found this nifty tool when a local boating store was going out of business. I love seltzer water, so I thought I would see how this worked. It comes with the carbonator, which injects CO2 into the water, a small container of CO2, and two bottles. Fill the bottles with water, press the buttons, and you've got carbonated water (club soda or seltzer, depending on your area.) I am totally hooked! I make at least 4 liters of carbonated water each day. I'm not dragging bottles home from the store and my water consumption has increased dramatically. I often throw a slice of lime in the glass, or flavor my drink with a splash of juice (or wine at night.) They also sell flavorings that make all sorts of sodas that are remarkably close to the name brands.
Once the machine is purchased, there is the ongoing cost of the CO2, which runs around $25 for a canister that is supposed to make 110 liters. (It seems to be roughly accurate.) I'm at my in-laws right now and didn't bring my carbonator, so I'm buying soda water. It is a pain hauling soda home from the store, the recycling bin is absurdly full, and I'm paying around $1 for 2 liters.
I'm sure there are all sorts of other things that are good investments. Please share!