.....net, after-tax dollars, or about $12,000 to $14,000 per year gross, before taxes. In other words, you could take a reduction in pay of nearly that amount to work nearby, and still have the same net left. The foregoing makes no allowance for the future at your present job, of course. Let me be the first to admit that good jobs are nearly impossible to find, but clearly something needs to be done here. That's a lot of exposure daily, and with increased exposure comes increased risk, inevitably. Difficult to quantify risk, however, and/or assign a dollar value to same, but it's there for sure, and it's your hide we're talking about here.
Re back situation, cheapest remedy I know of is to go to a bedding store and buy a 30" by 60" 'slab' of thick, orthopaedic foam rubber and bungee it into place on the driver's seat. Such a 'rig' will definitely soak up vibration and bumps, and give your back and bod one more chance to adjust to the seat. If that doesn't work, chiropractic is pretty much all you're left with. There are also acupuncture and 'rolfing,' (intense muscle manipulation); any or all of those treatment therapies may help, each in its own way, but plainly it's time to start trying different approaches to pain management. Remember, left untreated, bad situations tend to get worse, not better. Best of luck to you.