I just happened to be looking for one of these. Found an old thread from a year or so ago that had 1 color @ Amazon for $9.99. In the thread, people referred to a 2-pack deal @ Costco Business (currently $22.39). Search is failing me now, I can't find that old thread again.
Takeya has a 2-pack bundle on sale for $24.99. Use the coupon code: takeyatogether which is right on the home page for another 30% off. Shipping is free. Out the door price of $17.50. I was not charged sales tax to MA.