I posted a thread here about this very problem a few months ago after my $10 plan with Circles was bumped up to $15. I switched to an annual prepaid SIM with Catch, it works out to an equivalent of something like $7 a month for ~ 5 GB of data a month (plus unlimited standard calls/texts). Prices were pretty low back then due to EOFY sales but you might find it still works out cheaper now.
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If you can find an annual plan that fits your needs, and paying for a year at once is possible, that may work out cheaper per month.
It's been a while since I looked for a new plan, but it seems to me that the direction mobile plans are going is that the only differences are how much data and whether anything international is included. Most plans these days include unlimited calls and texts. As someone who doesn't do much calling or texting and needs like 2GB/month tops, pretty much everything has more than I need. A few years ago I was service hopping to whoever would give me a $10/month plan, but many of those have increased to $15/month.
The plan I'm currently on is no longer available to new customers, so unfortunately I can't recommend it to you.