I estimated that cost because my thought was that I would need to buy a steam set (valve assembly, wand and tip) of one of the commercial machines. Then a few more parts from home depot or something to connect that to the pressure cooker.

I used a steam capable gate valve with a bakelite handle and some ¼" brass fittings with a brass cap drilled as the home made steam tip. Cheap. Back then not lead free.

Thanks Kenneth. Good info. Good to know.

There was a guy who made his own steamer from a pressure cooker. -- EDIT: here it is!
Turning a pressure cooker into a dedicated milk steamer on demand

It looks really dangerous!

I have a stovetop bellman steamer (the steamer only, not the combo machine). It takes quite a long time to heat up the milk (60-120 seconds), and build technique. Results are decent, and if you are into doing the art, it can do it as well. I've had success from skim through half n half, and alternatives such as almond and home-made cashew milk (attached! my gf made that one, it's actually quite awesome tasting).

The steamer wand fells like it's on the wrong side, quite irritating. I'm in talks with a metal-working buddy of mine to see if we can modify the tip a little, maybe give it three holes or something. *shrug* Long way out, but has anyone done something like that, madifying a steam tip?

That's about what mine looked like except that I made a new opening in the lid for my valve. As long as the safety device is present and functional it should be safe enough. I also think there are smaller pressure cookers for such a project, mine was full size as the one on the other thread. I made at least one other for a gift. Talk about liability!!
KDM

A really good stand alone steamer is the one made by Haros from Australia. The photo shows it next to a Gaggia Baby, so you get an idea of it's size. It would pair up really nicely with a vintage commercial lever machine.