They really are quite affordable. The cost varies on the size of the box you want but you cant get much safer than a bank vault and you have the key.
Just don't lose your key. I have a friend that lost his key and it will cost him about $350 to get his opened. A locksmith has to come some distance to open it.
"... you cant get much safer than a bank vault and you have the key."
WRONG!!!!!!! The IRS can force the bank to open the box for them and then they can seize anything in it. Courts and lawyers can do the same.
Your home safe is the only solution.