Yes! There have definitely been times where I have ended up with lots of Buys and little money and wished there was some card/landscape/mechanism that would let me convert one to the other. (This probably says more about my ability than about the game's design, but still...)
Originally it was just an event (called Buying Power) that cost $0 and gave +$1, but I think that is too good a trade (or rather, it makes some cards like Market Square too good). This is how I tried to make a Buy worth approximately $0.5.
Here is the Event:
And the two-sided State it comes with:
BUYING POWER
Event
$0
If you do not already have it, take the State called Bull Market or Bear Market; whether or not you took it, flip it over.
BEAR MARKET
State (side 1)
Setup: In games using Buying Power, place one copy of this on the table with this side up.
BULL MARKET
State (side 2)
When you flip this over to this side, +$1.