You need to know the determinants of supply and demand for any future economics or policy work. I'll give you a few options for each here, other than price.
Determinants of supply
Input costs (price of oil, price of machines, wages, etc.)
Size of population (as it relates to the labor force)
Determinants of demand
Consumer's preferences for the ...
You said... "rates are often set by the Federal Reserve through manipulation of the money supply. To me, rates don't seem to change as a result of changes" in forces from actors that are not the Fed.
That's because the Fed succeeded in the time period you were examining.
If a thermostat keeps the temperature of the interior of a house at 20 degrees ...
There is one more element to take into account into this demand and supply schedule: how does the central bank conduct it's (traditional) monetary policy? There are two options:
decide on base money supplied and let the money market interest rate be determined endogenously as the money market equilibrium. In this case, for a given money multiplier, the ...
In the comments @henry already provided you with the correct conceptual answer, I will try to offer some extra intuition and way how this could be modeled. Currency exchange is a combination of a retail market with service market so here if you would want to visualize it with supply and demand you would have to use two diagrams for both parts of the market.
Are Price-Cost Markups Rising in the United States? A Discussion of the Evidence
According to this source market power is the ability of a firm or dealer to markup prices of output goods over the marginal cost of input factors.
The markup of price over marginal cost is a ...