[cleaning flux from PCBs]

I find that metho leaves a white stain on some PCBs.

Get out the meth's again & vigorously scrub the stained areas with an
old toothbrush. That usually does the trick for me.

Isopropyl alchohol is less likely to leave residue, but it costs a lot
more.

Not in the USA. 70% isopropyl alcohol (mixed with water, perfectly good for
defluxing) is 40 cents for 500 mL at the corner pharmacy.

How is isopropyl alcohol made and why is it so cheap and abundant in the USA
compared to other countries?