It depends on the type of media that you are trying to protect.
Floppies, tape cartridges, vcr tapes, etc. are much more succeptable to heat damage than CD/DVD media or USB drives.

Sentry rated for digital media (low temp)



A large number of their safes are rated for CD/DVD storage for 1/2 hour.

Sentry household fire safes (high temp. digital media)

Sentry product testing descriptions

Sam's Clubs currently have a chest size (about 15" w, d & h) for about $50.