Maybe I got this idk:
Money is always moving so there will always be some money to exchange for goods and such.
You buy a building - parts manufacturers and labor get paid... Labor at the very least uses that money for stuff and so on.
Without inflation the amount of money in circulation will probably decrease quite a bit. Yet as long as that money is divisible then the value goes up as civilization progresses and the amount in circulation keeps decreasing...
So a building will cost less money in a scarce money system as time goes on because the value of that money went way up...
Even if no one wants to spend anything and everyone sources their own needs... Eventually someone will want to buy something and it will be cheaper and cheaper as time goes on cause less money is moving... Money is scarce... More valuable... And it's measuring the value of civilization which is always progressing on average.