This depends entirely on if you are crafty or not. I make quilted trivets out of scrap material, quilt batting, and some sort of hard inside. I've used cardboard, plexiglass-type material, whatever.
You can google and find a pattern. I usually make a set of three and tie them up with a nice ribbon and attach a little trinket from the dollar store, kitchen related. They are fun and quirky, super cheap, and unique.
As far as a cheap "gotta get it on the way to the party" gift, I think the room diffusers are always nice.