Is there a decent standalone handgun safe out there that can hold, I don't know, 20 pistols or so? Fast access isn't really a concern. They are just starting to take up way too much space in my regular safe.
I use a 22x30x60" Cannon Oxbow safe. Its nothing fancy, but it keeps the kids and smash and grab crowd out. It was originally intended for a mix of hand and long guns totaling 34, but I have a bit more than that in it right now and I have room for probably at least 10 more .
Not much you can do to expand long gun capacity, but these rubber coated shelf racks work great and they are cheap. I think I got these at Wal-mart, can't remember the brand. Different brands have different spacing, which works with different guns depending on the width. So you may have to shop around a little. I think on some of them I hack sawed the legs down a bit to fit on the shelf in my safe, leaving just enough height so that that the tip of the barrel remains off the safe shelf.
Actually, since these photos I found some black ones with slightly wider spacing that seems to hold the guns better.
A lot depends on how you're going to store them. Something like jad0110 is suggesting would help you get by with a much smaller box.
You might look around for a business that is closing and see if they have a safe they're going me to sell. A lot of times you can pick up a really high-security safe (not just an RSC) at a really low price. Most aren't big enough for long guns, but you can probably find one that will hold that many handguns.