Well I mean it like this
Carry on bag and personal item: Free
Board bag (first checked bag): 25.00
Additional bag if needed: 35.00 (I think)
It may have changed but I flew with them this past March so it hasn't been too long since. I saw a skier have his boots attached around the strap of his carry on bag but I personally had my boots inside the carry on bag with shirts, unders and gloves shoved inside the boots. Saw other people with tons of stuff tucked into jacket pockets. If it seems like stuff wont fit, roll it.
Might want to check this link out to be sure, like I said airlines tend to change their baggage policies fairly often
United Airlines - Checked Baggage Service Charges