Total price for me was about $64. Most expensive part was the O2 regulator.
After you chill the wort, but before pitching the yeast, you need to aerate. Otherwise the yeast won't be able to do its business. For years, I tried things like shaking the fermenter or stirring like a madman. Then I read an article saying that one of the biggest things you can do to make better beer is to pump in oxygen. Here is the device I made to to it.
Step 1: Cut Pex & Instert Stone
Cut your pex tubing long enough so it easily reaches bottom of your carboy or bucket. At first I tried just regular flexible tubing (the stuff they sell in coils and bends really easily), but when it went into my carboys it curled up and would never reach the bottom. While pex is 'flexible', it is rigid enough so it can hold the aerating stone wherever you want it.
The stone barb is 1/4" and so is the pex.. I couldn't force the barb into the tubing at room temperature, so I stuck that end in some boiling water for 5 minutes . When the tubing was hot, I was able to get the barbs all into it (see pic). Don't burn your hands; use a towel or oven mitt to hold the hot tubing.
Step 2: Connect Tubes
Set up the sleeve & compression fitting as shown...
I used 5/8" and 9/16" wrenches to tighten up the fitting. Now that I'm done, I wonder if I should have used one of the plastic sleeves that came with the insert. When I turn it on, I hear no leaks, and the stone bubbles in water, so I'm not going to worry about it.
Step 3: Done
Connect the tubing to the regulator and you're done.