My solution would be don't drive or ride the bus. Sorry, but I would never ever risk my childrens lives like that regardless of my financial situation. Where there is a will there is a way. I firmly believe that.
You risk your child's lives every time you put them in the car, regardless of how well they are restrained, simply because not all crashes are survivable. They're also at risk in a wide variety of other ways. "Safe" isn't a real word, because none of us are ever truly "safe." There's risky and riskier and safer and safest, but there's no black-and-white.
Not all towns have public transportation. Practicality has to factor in at some point. It's easy to say you'd walk instead, but if you live 4 miles from the grocery store, and only half the route has sidewalks, and you have three kids and the oldest is 5, and there's six inches of slushy snow, not to mention your oldest lost his winter coat... at some point you're going to have to decide whether the risk of getting in a crash while your children aren't in the safest restraints truly outweighs their need for food, diapers, and medications. Not to mention the risk of getting hit by a car while walking along the slushy snow-covered road with no sidewalks.
Every child is at risk for injury and death, whether or not they're in properly-installed carseats or never ride in a car. As carseat techs, our job is to help parents assess that level of risk and make decisions to decrease the risk. But we'll never be able to make that risk go away completely.