It's not that simple. If a poor person makes zero dollars how much of the reduced cost item could they now afford?

We have a massively distorted economy driven by debt financialization and legalised banking cartels. It leads to weird inversions. For example as long as housing gets increasingly expensive at a predictable rate the housing becomes more affordable instead of less as banks are more able to lend money. The inverse is also true, if housing were to drop at a predictable rate fewer people would be able to get a mortgage on the house so fewer people could afford to buy one. Housing won't drop below cost of materials and labor (ignoring people dumping housing to get rid of tax debts as I would include such obligations in the cost of acquisition). Long term it's not sustainable but long term is multi-generational.

Or the goods will just go away if too few people are willing to pay their price, and only the lower-quality cheaper-to-make goods will remain.

"will" being the operative word here. High school level Econ makes no promises about WHEN prices adjust. Price setting is a whole science highly susceptible to collusion pressure. Prices generally drop only when the main competition point is price (commodities). In this case the main issue is that AI is commoditizing many if not all types of labor AND product. In a world where nothing has value how does anything get done?

This and other fairytales.

The only solution here is to stop tying people's value to their productivity. That makes a lot of sense in the 1900s but it makes a lot less sense when the primary faucet of productivity is automation. If you insist on tying a person's fundamental right to a decent and secure life to their productivity and then take away their ability to be productive you're left with a permenant and growing underclass of undesirables and an increasingly slim pantheon of demigods at the top.

We have written like, an ocean of scifi about this very subject and somehow we still fail to properly consider this as a likely outcome.

Cool concept, but this isn't 1980. We've been sold these sorts of concepts for 40+ years now and things have only gotten worse.

We have a K shaped economy. Top earners take the majority. The top 20% make up 63% of all spending, and the top 10% accounted for more than 49%. The highest on record. Businesses adapt to reality and target the best market, in this case the top 10 to 20%, and the rest just get ignored, like in many countries around the world.

All that unlocked money? In a K shaped economy it mostly goes to those at the top, who look to new places to park/invest it, raising housing prices, moving the squeeze of excess capital looking for gains to places like nursing homes and veterinary offices. That doesn't result in prices going down, but in them going up.

The benefit to the average American will be more capital in the top earners' hands looking for more ways to do VC style squeezes in markets previously not as ruthless but worth moving to now as there are less and less 'untapped' areas to squeeze (because the top 10-20% need more places to park more capital). The US now has more VC funds than McDonalds.

I don't know what economy you are looking at, because the opposite is usually true since humanity industrialized.

If goods aren't being sold, then the price will increase.

to the point of where the cost of bringing the goods to market or its opportunity cost exceed the price the market will bear. Its why people living in areas of material poverty don't just get everything on discount.