I haven't posted here regularly in a very long time, but I thought I had to come back and share this.
I finally made myself a T-handle. Every now and then the idea would pop up to do it again, but for whatever reason I'd run into a real or imagined roadblock and put it the idea aside. The 2 or 3 times I actually went out to get the materials in that time the hardware store just didn't have any stock, or were missing a specific piece, or the wrong diameter, etc. Today I literally walked straight into a shelf full of galvanized steel pipe nipples and flanges, so I dumped all the parts in my trolley and spent the $28.
To give you and idea of the value, this holds as much as 40kg of weight with the plates I've got (could hold probably fit as much as 80kg if I used 10kg plates). For a 40kg kettlebell I'd be looking at around $120, not including delivery. For an adjustable kettlebell I'd be looking, insanely, at ~$220.
Simplest and one of the cheapest things I've ever made.