Welcome to FT!

Do you only want to fly nonstop, or are you OK with connections?
​​​​​​
For nonstops, your only options from DSM are Allegiant, Frontier, and Southwest. Given those choices, I would just pay cash on Southwest, which will give you each two free checked bags, if needed.

If you're willing to connect, plenty of options with AA, DL, and UA. With MR points, you could transfer to Air Canada Aeroplan or Avianca LifeMiles -- among others -- to redeem for "Saver" award seats on UA -- if you can find them. For DL, you can transfer MR points directly to Delta, but Amex charges a fee to transfer MR points to domestic FFPs. You could also transfer to one of DL's international partners to avoid the Amex transfer fee, but the redemption rate might be more (or less) than what DL would charge directly.

Under your circumstances, I do not see a compelling reason to drive to a more distant airport.

Good luck!