I don't know if it costs less than $100 but here is a good solid deadbolt that I have seen used in quite a few applications...
The Kaba-Ilco (formerly Lori) Mortise Deadbolt --
http://www.kaba-ilco.com/key_systems/pr ... aspx?id=35You can install any standard size mortise cylinder you can obtain in the proper cylinder length... A locksmith can easily obtain these deadbolts through their supply house...
I have seen one of these deadbolts installed with the optional drive in bolt (no rectangular plate for the bolt with screws on the edge of the door but instead just the round bolt) used on a metal rear service door at a retail establishment where the door was beaten and bashed repeatedly and then pried but entry was not made... The lock was broken but it still held the door closed... It was amazing to see a door in that condition still locked but it held...
Obviously these locks will not magically hold a wooden or sheet metal clad residential grade door closed under such an attack but they are a step up from the stuff sold at the big box home centers...
~~ Evan