It came out to about 17-20 bucks by the instructions I used, a little under 10 bucks for the parts and about 7 for a tap to tap a cap, a #60 really frickin small drill bit, and some teflon tape. Also, the >10 figure included a bag of 4 springs when I only needed one, and I just picked up some more ball bearings from the bike shop because they're really cheap, so I could build 3 more of these things at a cost to myself of like 6-7 dollars.

One thing, HDPE really let me down, I had to drag my ass halfway around that dang store and back again to try to find all the parts, and eventually had to go to the bike store and to ace hardware to find half of the stuff I needed, plus they didn't have the best kind of npt tee so I got stuck using a backup that lets the spring deflect more. HDPE gets two thumbs down on this one.