Ed, I'm not prepping for/with a disability but I am on a tight budget. Some of the things that work for our family include:
*Absorb wisdom. There are A LOT of experts out there, who will tell you exactly what you need to do to prepare for an emergency. Some of them are full of poop. Research with an open mind, but keep your BS detector on. It's easy to get overwhelmed and caught up in an extreme mindset. Think seriously about what you really need to prepare for. How likely is any given scenario? How big of an impact would it have on you/your family? When I first started preparing, ETS was a HUGE help for me in this regard. The people here are pretty realistic in their approach and I really appreciate that they help me learn and keep me focused at the same time.
As an example: the top four likely events that my family prepares for are house fire, local industrial emergency, local weather emergency, and job loss. An emergency at one of the nuclear plants near us would have devastating consequences for us, so we prepare for that too, but the likelihood of that happening is lower, so we have KI pills and keep our vehicle gas tanks full. The concrete bunker filled with guns and gas masks, that I was sure we needed when I first started prepping, has been moved way down the priority list.
*Don't go buying fancy stuff for bug-out bags or bug-in supplies until you know what you need and know you can afford it. Make a list and look around your own house first. Clothing, blankets, cooking stuff, hygiene, etc... you are probably more prepared than you think. Organize what you have on-hand first, and then make a list of what you need.
Once upon a time, my husband and I bought a years worth of food. We took delivery up-front and we paid for monthly over the year. The pantry and chest freezer were full and it gave us great peace of mind. (It sure came in handy when my husband lost his job.) At the time, we could afford it, and we made it last a very long time by continuing to do our regular grocery shopping every week and rotating the goods through the pantry to keep everything fresh.
We can't afford that anymore, so now I buy a little extra every week when I do my regular grocery shopping. A few extra cans a every week doesn't break the bank and will add up quickly.
*Make a smart budget and stick to it relentlessly. Save for big ticket items and shop the sales for the little stuff. It really helps make the most of our money. If I allow myself $5 a week to add to the emergency pantry, for example, I can spend $1 a can and get five of something, or look for a sale and get 2 for $1 and double my purchasing/storing power.
*Storing only what we actually eat. We don't have specialty food for emergencies. (An emergency is going to be stressful enough without asking my kids to eat something different.) We do have some fancy dehydrated meals and MREs, left-over from our days of having a disposable income, but dehydrating or canning home cooked meals in the oven is way cheaper and healthier.
*Eating what we store. Buy stuff when it's on sale and rotate through your pantry from oldest to newest. It'll help keep your stored food from going rancid, and you'll always eat at good prices.
*Learn to cook. It's cheaper and cooking for yourself is a survival skill all on it's own. Practice making meals without the convenience of electricity. In fact, learn to use all your emergency supplies and practice your contingencies. Monthly fire drills at home, power-free nights at home, mock bug-outs.... being ready includes knowing what to expect, as best you can anyway.
EDIT: It's not budgetary in nature, but I'd also add learning your medical needs and procedures to the "Learn to Cook" theory. If your medical services are not available in an emergency, you need to know what you need to do to provide them for yourself.
*Don't buy water. Clean your own containers and refill them with tap water. Add a little bleach if you're concerned about germs.
*Second-hand stores and garage sales are great for finding supplies. You can often get great quality stuff for little money.
*Dollar stores are great. The quality/quantities aren't always the same but you can find good deals there on all kinds of things.