Interesting concept. $20 for 5 dice is within reason, but if you wanted to get the different sets could add up quick. They also make a
set of cards that do the same thing, but you get a 90 card deck for $15. Probably more practical and economical. Frankly in this day and age, there is probably an app for a phone that does this. If not, it would not be hard to code.
But there is an awfully high novelty value on dice. “You open the door and see <rattle rattle> an alter room"