How can I find the price (not just the yield) of a treasury bond?
Price is what you pay, yield is what you get. The advantage of looking at yields is that they make it easy to compare different bond issuances. The price of a bond will depend on the face value (generally $1,000), coupon rate (if any), payment frequency (annual/semi-annual), time to maturity, and discount rate. If we're talking about the dirty price, rather than the clean price, we'll also need to account for the accrued interest since the last coupon payment. If you have the required inputs, you can compute the price using the present value function of your calculator or spreadsheet software. That said, Treasury Direct let's you request historical prices by date.