Most sheet metal shops can bend you a box for less than $100, I was talking to one of my local places, they offered to make me a 1/4 Hard Ox safe, but that has to be fabricated from plate steel, so about $200, but 1/4 non-mild steel is the MINIMUM to get an actual UL safe rating, and not a "residential security box" (most "gun" safes) The only problem was that I couldn't figure out the lock mounting, and a S&G lock cost about $100, so all told, you could make your own safe for less than $500 that kicks the **** of some $2000 name brand. That includes paint (auto body shop, fire lining and shelve system)
On the other hand, a nice gun case shows that want to keep honest people out of your guns, and takes about as long to break as "gun" safe.
Read some articles about gun cabinets and safes, you want a minimum depth to keep it from tipping over easily, a 4' by 1' is dangerous as it could tip over and squash a little 2 year old pulling on the handles.