The above places suggested places are excellent sources as well. While you are looking check for other senior programs that may be available, even food stamps, and there are programs that help with heat and electricity. It's not a lot but helps
Try this link. It's for Senior Health Assistance Program. They should be able to provide info of who can help.
It's a long list of places broken down by counties. Gives addresses and phone numbers.
DO NOT try to do it yourself. You would have the cost of shingles, nails, disposal of old shingles, other roof repairs as needed, tar paper that goes under the shingles if needed. Been through it when younger and it's not easy. The stuff is very heavy. Two trips in small pickup to get supplies and I forget how many to dump the old shingles. Broke wheel on the large (super cans) city used for trash. I was not on the roof, a friend did it for us. Not long after that he fell off a roof and broke his back.