If you give everyone $600 extra I would bet that things like rental costs, utilities, etc. would just expand to take the extra money.
The extra money would then be collected into the company providing those services. If it just sits there, then it can get taxed at a higher rate (cause the government can play that game too.) If it is instead paid out to workers, that increases the worker's wages perhaps even more than normally obtained through UBI. If it is instead used to hire new workers, then that fixes unemployment. Stockholders of some companies may also demand dividends from the company's surplus funds that just sit there.
Also, in a free market, there's some companies that might not increase prices, and instead get additional profit from volume rather than scalping.
Speaking of price inflation, why doesn't Alaska suffer from massive price increases due to the Alaska Permanent Fund? Also, why don't prices likewise increase because of existing welfare programs?
Governments already have systems in place to handle monopolies by now, especially if it's on an important resource. If not, then maybe the government should take control of said monopoly just to reap the benefits.