I have a couple thoughts on this:
First of all, don't get into your paranoia too deeply. We all know the world is coming apart at the seams, why make it worse by worrying. Instead, know that you are tempting target to the have-nots and make an inventory of all your stuff. Make sure that you have up to date insurance and know that be they zombies or (illegal) aliens, someone who is set on breaking in will get in. This is a zen way of looking at break ins, whatever you have taken, you shouldn't really care about anyway and be ready with a backup plan.
Second of all, do not set boobie traps
. I've been extremely tempted to do this in the past, but they are pretty damned illegal since they do not discriminate between actual threats and "fake" threats. Though, I always think, if they are in your house or your yard without permission, electro-zap/jaw-leg-hold away, I've never actually implemented it.
Third of all, if you shoot someone in self defense, you should make sure they are really really dead, otherwise they'll sue you. Preferably, have the wife do it since she's probably more sympathetic than you in a trial.
Most of all, breaking in is usually done by lazy, stupid people. Make sure all your locks are in working order and always lock the door and windows when leaving the house.
From my ghetto to yours, klari
PS. I don't know the costs, but a safe might be useful for the papers.