I may have seen that thread, and it probably gave me the idea for my second option. Still, I've got to wonder about the relative hassle-insecurity of a cheap MVNO versus GVoice. Like sure Google has a bad rep, but at least they've got good common-case security properties. Whereas a lowest bidder MVNO is likely to have poor security to begin with, and poor customer service for cleaning up after the fact. It might still be worth it to try a GVoice number first for every service, then fall back to the mule. (although everpresent point against Google: they're better at exploiting surveillance data, in a way that an MVNO won't be)

"all of these phones" implies you have expanded to multiple mules? I presume for multiple accounts at the same service? Is there any indication that really works for eg making it so all your Google accounts don't get locked at once? Or are you doing it to undermine the use of phone numbers for cross-service surveillance association?

FWIW I haven't looked in a while, but the cheapest US consumer SIM I've found is H2O Wireless (on AT&T) at $10 per 3 months.