That's an argument as absurd as claiming A+B+C+D+E+1=5. You don't know what each variable is, especially not without actually looking into them.
You also may as well just say that we can't give the bottom 80% a raise, even though the top 20% has been getting a raise for decades, because if we did, all prices would go up.
When was the last time you told your employer to go ahead and skip giving you that raise, because you'd just end up spending it on the increased costs of goods and services anyways?
Competition still exists with UBI. In fact competition is enhanced with UBI. It would be pretty stupid to raise prices in a competitive environment, right? Would you raise your prices as a business owner, knowing full well that it would only make Amazon look even more attractive?