The market won't change too much. Everyone can afford food and shelter and clothes now, in the former 1st world countries. There are places in the world where people can't get food and thus die in the streets, but this is a rounding error here. Therefore not much will change at the bottom end. Prices might drop slightly due to reduced demand because people will occasionally splurge.

Note that this won't actually help with many social problems. For example kids who go to school hungry because mom spent todays money on crack will after UBI merely go to school hungry because mom spent todays money plus UBI on crack. Neither the slumlord nor the supermarket will see a penny more. Cultural changes are much harder to make than mere economic changes.

If competition works, companies won't be able to hike the price of necessities.

If competition doesn't work, the entire premise of capitalism is unsound.

With markets. As the distribution of income changes so does the distribution of goods and services produced.

The UBI can be scaled by the cost of living index which will shelter it from inflation. We have a sovereign money supply for a reason. Let's use it!

I keep seeing people say use the cost of living index. Do any of you realize what a fraud that is? They have taken out the two most expensive categories people spend money on to survive. Food and energy. And it's been like that for decades. That index is as useless as tits on a tree.

It can be tied directly to inflation or even to GDP. See details here: https://medium.com/basic-income/wouldnt-unconditional-basic-...