Wow. This comment isn't going to be any help to you, but I thought it worth noting.
In most things technological - almost all things - costs in the UK seem to be considerably greater than the US. Often we are paying the same number, except for me it is in pounds, not dollars (so about 41% up).
Why this subject is worthy of note is that the prices given here are about inline with what the major carriers would charge for a bundled phone + service.
However, we have a company called GiffGaff here, which started off as a community organisation, using the O2 network here. It is now owned by O2, but run independently, and customer support is still done via online community.
GiffGaff will sell you a phone, but their main business is in SIM only deals, assuming you have a suitable phone already. Their cheapest rate is £6 ($8.50) a month, for unlimited calls and texts and 500Mb of data a month.
I am on a continuing (i.e. self-ordering) rate of £10 ($14). This gives me unlimited calls and texts and 10Gb of data a month.
Yes, you do need to buy your phone on top of this, but it is then yours to keep or replace as you see fit, not because of any contract. My phone - a Moto G6 - cost me just over 200 quid, and is now 3 years old and going strong. I would have paid for it twice over in a bundled deal.
GiffGaff has had this market sewn up until recently, when a new similar company (also backed by one of the big mobile companies) has appeared, called Smarty. Smarty has even better deals, but I'm content with GiffGaff for now. However, it is clear that the new market in the UK involves selling the old expensive bundles to those who know no different, while offering the cut price SIM-only packages to those who look for a deal. So they get two bites of the cherry, and by splitting it off into another company, they aren't accused of having predatory rates.
I'm really surprised that something similar hasn't appeared in the US. Give it time, I reckon.