If you are planning to "bug in" preparedness is almost free. Where I live, in Hurricane country, preparedness is an annual event. I can't bug out, minus an ocean going boat, as the roads will be clogged. So the bugout bag is just a backpack with 5 days food, a camp stove, tent, water filter, bag and raingear and weapons and money (hidden). The extreme "bug out" is the extended camping trip in the Glades. There, its what I can fit in a canoe.
Real life? I prep for 30 days cut off. This is easy and cheap. A good first aid kit (bought piece meal, not off the shelf, figure $150)'
Food, as others have said, buy stuff you'll eat anyway. Rice, beans, diced tomatoes, corn, kippers, no-refrig bacon, just add water pancake mix, and ramen etc.. If you don't use it? Donate it at Thanksgiving and and restock. It really doesn't cost much. No pricy MREs. Just buy 4 rather than one and keep the larder up.
Same deal with water. The rule is one gallon per man, per day. I keep thirty gallons of water bottles and rotate as I drink. Its not much of an extra cost.
As far as flushing? Buy 5 5 gallon buckets, $.75 each at the dollar store. I live on a golf course and have a pond in the back yard. No problem.
I bought a bunch of battery lanterns and a ton of flashlights (figure $150 if you're not a light nerd, and less is easy). Every two years I hit Sams and buy a bunch of Duracells (maybe $150).
As far as cooking? I've got a Weber and a campstove. I use them anyway. Cost? $0.
My only luxury is a Honda propane generator and 11 bottles of gas. That's about $2000 and will get me through two to three weeks. I've also got the gas to use on the grill. So discount that by the propane bill.
Basically, I'm good in my house for a month. I really am out very little money per year, as most of what I buy, minus the generator and batteries, and stuff like ramen and instant mashed potatoes, gets used anyway.
The bugout gear and first aid kit are a different story. But, if you are like me and plan on hunkering down for lack of a better option; staying warm, dry, and fed needn't be all that daunting. If you have to move? Well, that's a whole different game. I can talk about it, but here in South Florida, unless you've got a boat, demographics and geography are against you.

FQ13