Toxilicks
On one hand, your body, your choice.
Assuming you're not blowing smoke, you don't sound like you're thinking this rationally. "We can do anything we set our minds to" isn't enough, you need to have an actual plan, a budget, and apparently you're scrounging by at 28k, and that isn't a lot, let alone to support four mouths, taxes, bills, rent(?), etc.
If you don't abort the fetus, at least consider giving it up for adoption, unless you and your husband can reach some conclusion where three kids may not put you in jeapordy.
This, OP.
You need to stop thinking about how much YOU want the baby. You have a family and you need to make family decisions TOGETHER. You say you're a stay at home mom, and that he's the breadwinner; it sounds like he's concerned with your family's current budget. How involved are you with the budget exactly? Like, do you know how much it is for the care of each of your current children, your mortgage/rent, health insurance, care insurance, etc?
I understand you're upset because you want this, but please, think over things from your husband's point of view. Take a deep breath and step back and evaluate everything that's involved with going through with this pregnancy. Look at ALL of your options--look into adoption like Toxi suggested.