Amazon has the Skylanders Swap Force starter pack for $19.95 if you need the Playstation 4 platform. This is a great price but I’m not sure how long it will last. Just make sure to click on the PS4 to see the price.
Hopefully they will drop the prices on some of the other platforms.
If you order now and select two day shipping (free with Prime), this will arrive by Christmas.
Another option is Target. It is slightly higher at $31.99 for PS4 but shipping is free and you can select in store pickup to get this sooner.