Yikes! I'm also confuse now..
ok here's the deal.. the fare on Expedia for that particular route is about $100 cheaper than on UA website.
so I have basically 2 options right? Buy the Expedia one using my Mileage Plus CC and hopefully get some miles from that purchase.

Option 2. Use my exisiting miles to buy the UA one even though it's more expensive. The problem is how do I know if my exisiting miles cover the UA flight?

How do I determine which is a 'better' deal in terms of a combination of miles and actual $$ spent?

hope that make sense.. or not LOL