Thank you for all the info. Unfortunately I used up all the points and miles for my recent trips. There are some options (Arriving 1AM in SLC and Red eye flight back to ATL). However, with two kids I would like to avoid those options.
With all your advice, my plan is to check regulary until the booking windows of WN and Frontier open. I hope I can find the flight pair within my accpetable price range sometime this spring.
Oh. I reserved rental car. Thanks.