Mint [1], is $20/mo for unlimited data (throttled after 8GB), using the T-Mobile network. You get a discount for committing to a time period such as 1 year.
Visible [2] is $40/mo for "unlimited everything" (data, calls, text). This is Verizon's low-cost product on their own network.
Simple [3] is $40/mo for 15 GB, also using T-Mobile. You're throttled to 2G after that, though.
These are MVNOs, which are resellers that don't own their own networks. Traffic is deprioritized compared to the parent network's "native" customers. In practice, you might not notice at all, depending on how you use it. Deprioritization really only happens during congestion. During rush hour on the NYC subway might be a time you'd be affected, for example.
Partly that could be explained by lower population density.
Also services like Visible started to appear. They offer unlimited talk and data for $40.
[1] https://www.vodafone.com.au/plans/state/sim/month-to-month/
Maybe "insane" was a bad word choice. But it's more than triple the price (£20 is $25, not $30, and $70 excludes tax)
In the UK, it's hard to spend more than £20/month (for sim only at least)