Birth control question for the married, income challenged, uninsured, and not in the best physical health?

I've been with my husband for 15 years, although we've only been married for 7 (I'm only 29, until May). We have 3 children. I wanted to get my tubes tied after our third, but it didn't happen because of timing issues. We are low income, and I don't have insurance. We don't feel comfortable with condoms. Due to blood pressure issues, weight issues, and chronic headaches, I cannot take any hormone-based birth control such as the Pill or the shot. For the last two years, we have relied solely on the timing and withdrawal methods, which I know are not that reliable. I would not mind having my tubes tied, and I may even be able to talk my husband into a vasectomy, but neither of those are an option due to cost issues. Is there anything we can do that we can afford that will not ruin our wonderful life or give me a heart attack or stroke? Serious answers only please. For the last several years, our life has been lukewarm at best. But as I approach 30, I am finding a renewed love for physical intimacy which has brought our lovemaking to new heights. But our third child is finally out of diapers and about to start preschool and I do not want any more babies any time soon, if ever. What can we do?