I picked up a Trek 400 series last week that has the same crankset as your black bike above. Using the information on serial numbers from the Vintage Trek webpage (http://www.vintage-trek.com/) I found that it was built in 1985.

Since both of yours have Aero style brake handles, I assume they must be a little newer than '85 (I have an '89 with a set up very similar to the blue bike).

I'm sure you'll find a taker on buying the blue bike. $100 plus shipping is very reasonable.