I agree food is your main area you can make a difference in w/the income you're already bringing in.
Try:
http://www.menus4moms.com/frugal/mea...rd_times_1.php
and
http://www.hillbillyhousewife.com
If this is too austere for you try cycling on and off it every week to 2 weeks and see if you can't put back the savings for your Emergency Fund.
With that bad knee you might try the paper-route idea. Also in our state we have a vocational-rehabilitation program that will help send you to school so you can get training for a job that will allow you to stay off whatever injured or disabled body part you've got. You might want to look into something like that if you're wanting to go to school yourself.