After much google searching, I finally found a link that offers FREE printable premade treasure hunts. Lots of places will sell them to you. Lots of links turn out to be junk.
But here is the best site I've found - Reading Clues Scavenger Hunts and Treasure Hunts. I used the Inside Rhyme Hunt for my younger two (ages 6 and 8).
They have pre-reading (picture) hunts and text-based hunts as well, both scavenger hunts (kids look for stuff on a list) and treasure hunts (you hide the clues and a prize at the end).
I also found this site with tips on making a Bible treasure hunt and the beginning of a hunt started for you. I used this one for my older two (ages 11 and 13). I used the clues they had and then made several more, using Bible Gateway's search feature to find appropriate verses. [Note - 2 of the sample verse references are incorrect, so if you use the samples, please doublecheck them.]
I'm off to do the treasure hunts soon! I'll let you know how it goes!