I mailed out a DVD (single disc) and asked for cheapest way (priority or media) -- it went media mail so I paid $2.69.  I thought I used to get a cheaper rate for DVDs but don't know  since I haven't mailed out a DVD in a long time.

First Class probably would have been cheaper, though I am not familiar with the post office prices since I ship everything online. SwapaCD allows people to ship the CD without a case, as a first class non-machinable letter, but they break often like that, as you might imagine. 

as a general rule I think anything 8 oz or below is cheaper 1st class if you use online postage like paypal. since paypal has no fees it is the best way to ship 1st class. 8 oz 1st class is 2.59 on paypal and online has free tracking.

Think the DVD in a normal case (not small CD case) could not go 1st class cause it wasn't 'flat'.  

I always use First Class package when mailing DVDs.  First Class costs less than media mail.  I prefer electronic postage for a discount and free tracking.  Most single DVDs weigh 4oz, 3oz for a Eco case,  5oz for a Blockbuster case. It's $2.09 for a 5oz package. 

If you mail a CD in a jewel case that should be a First Class package.  For the Letter rate it must be flat (no more than 1/4-inch thick). Send the disc in a birthday card envelope with cardboard 2 oz = 70¢ + 21¢ non-machinable = 91¢ or use 2 forever stamps (worth 98¢).