The suffix after the part number specifies the package the part it in (e.g., T0220, TO92, SOIC-8). The data sheet is your friend.
Searching for LM2931 on Octopart.com shows some of the different options - see first picture below.
Clicking on one of the TO92 versions available at Arrow brings up the price breakdown for this part and a BUY button. See the second picture below.
Clicking the BUY button brings up the screen where you can actually purchase the part. Enter the quantity you'd like to order, and click the BUY button. Note that the screen says Overnight shipping is free. If you click any other option when checking out, shipping will not be free.
Once the desired parts are in your cart, click the cart and select check out.
View attachment 115905View attachment 115906View attachment 115907View attachment 115909
I can find lots of cheap prices, when you add $10 postage to a 49 cent part the price is $10.49
Nice thing about 10% and 20% resistors, I needed a 160K resistor all I have is several 150K resistors, one resistor reads 160K on both meters. Same thing with 30K resistor all I have are several 33k resistors, 1 reads right on 30K. I test every part before I use it to make sure it works and value is right.