Sensory mats - "Goo bags - recipe for goo. I've had it suggested to use an entire bottle of dollar store hair gel, but this is probably just as inexpensive, and you can make whatever VIBRANT colours you want." Letter writing with fingers or Q-tips.
Safe Sensory Play - even baby can PLAY! These flakes are very inexpensive, have a super fun texture, and are edible, making them safe for even the tiniest tots. For under one dollar you can fill a sensory table or bin with these flakes and kids can play