Hello there, from one Oregonian to another.
I'm glad you decided against the Kangaroo boosters, I would not put my child in one. They also aren't terribly narrow (to fit three-across).
About your 93 Escort: it only has a lapbelt in the middle, correct? If so, the only thing safe there is a harnessed seat. A lapbelt only prevents ejection from a vehicle, it does not restrain the upper body at all, which can cause serious injuries in a crash. A booster should
never be used in a lapbelt-only spot. All boosters require a shoulderbelt to restrain the child's upper body. It's actually more dangerous to put a child in a booster with a lapbelt than to put the child in the lapbelt alone.
Since you qualify for food stamp benefits you should be able to get free/low cost
new seats from someplace like a county health department. Most carseat inspection stations also have free/low-cost seats available for those who meet income guidelines.
The Kyle David Miller Foundation might also be a place to apply for a free seat. Income restrictions apply, and the wait list can be long sometimes, but it might be worth it to at least look into that option. I'm helping a local KDMF recipient family in the very near future.
Since you have a lapbelt-only position to deal with, I'd really, really try to get a (new, not used, unless you trust the owner of the seat with your child's life) harnessed seat for the 4.5yo. Otherwise, you have to make some tough decisions and choose to place one passenger in a lapbelt-only spot with little crash protection.
BTW, we were also on food stamps and living on $8 an hour when we got our first higher weight limit harnessed seat to deal with a lapbelt-only spot, so I know how tough it can be. ((hugs))