Originally Posted by
flyingeph12
Could you fly into COS and drive up to DEN (it's about a 90 min drive without traffic)?

Didn't think of this earlier, but particularly if you are located north of Chicago, you could start from MKE and go through DFW. The DFW-DEN flight shows Y4, but there appear to be plenty of unassigned seats (presumably a lot of people booked on a Basic Economy fare, didn't want to pay for a premium seat, or otherwise have unassigned seats).