> There is no argument here -- why would everything cost $1000 extra?
Because you can't print food, houses, energy etc. Give everyone $1000 and you won't magically create any more food or any more houses or any more energy out of thin air. So the market will adjust the price to account for the increased demand. It's basic supply and demand.
> If everyone gets $1000 as UBI, then those 500 lollipops will cost ... $1001 each and $501000 in total?
> Isn't that absurd?
Yes it is, but you misunderstand. It's not that every individual item would cost $1000 extra, it's that the total cost of living would be $1000 extra.