If you have the will and means to move them, you can usually pick up antique safes and jewler’s vaults for free, or nearly free. I have one that weighs roughly 2600 lb., in which we keep most of our small valuables. It’s a Yale Safe jewelers vault built in the later half of the 1800’s, and still plenty secure today.
Gun safes are also a good option, if you need some serious volume. Most aren’t super secure, but they’re good enough to keep someone at bay awhile, if you have a home security system to dispatch police. Most of the better ones also offer reasonable protection from fire.