i'm in aspen frequently and have found the molly gibson to be reasonable, also the inn at aspen has good rates. a little on the steeper side is sky hotel, by far my favorite, but a bit more.
one thing to remember, i find the girls at the abo concierge desk to be absolutely useless in finding cheap digs. it seems they get a commision and stear you to a small list of hotels.
also there are two property management companiesin aspen we use occassionally but i forget their names at the moment. good luck...