Not sure if this applies to you, but 5th and 6th graders can ski for FREE at many Colorado resorts! We participated in this and it was fantastic. You do need to plan in advance since you have to send in proof of their grade level (such as report card) and they will receive a ski passport in the mail. 5th graders get 3 free days at each resort and 6th graders get 4!
http://www.coloradoski.com/passport
Look into booking through VRBO. Ask the owner if they can tell you how to get deals/coupons. They will have all the inside info. and will be happy to share it with you.
You will save lots if you decide to stay offsite. I have never stayed at the base of the mountain and it's never bothered me at all.
fly into Denver and stop at a grocery store before heading into the mountains. Stock up on stuff to cook meals and pack lunches for the slopes. The food at the ski resorts is so expensive, not very good, and the lines are usually long.
Look into smaller resorts in CO. We have never checked them out, but have decided we will look into it next time. We know lots of people who have done this and say it's plenty of skiing for beginner/intermediate.
Consider inviting another family to join you. Splitting the lodging expense helps a lot!