[ccarpenterg]

Interest rates are the price of capital

I think that's inaccurate. The price of the capital is its cost of opportunity. Interest rates are the price of debt.

[chimeracoder]

No, interest rates are both. All costs are opportunity costs, so it's just two ways of looking at the same coin.

[capex]

Interest rate (ideally) = rate of inflation + the risk involved + cost of opportunity.