Your best resource for finding hotels in and around Boulder (with a discount) is to visit the "Travel" page on the Boulderthon website. They have partnered with HotelPlanner to offer discounted rates for the weekend of the race.

Unfortunately, most of the hotels that are walkable to the race site are going to be $$ (it's also a CU-Boulder football weekend), but it’s super easy to get around town and you can stay just outside of Boulder (10-20 min drive) and save a lot! Also - if you book a longer stay (Fri through Mon, for example), you'll find the rates go down compared to leaving on Sunday.