Hi Paul,
Good to see you are keeping an eye on us!!
I hope you have been keeping well.
It's probably the case that the OP may not have been 100% serious about the comparison, hence not 100% accurate with the economics. Or maybe not!
Your point about stimulating the auto industry is surely correct, and the main reason you would spend such a sum, not purely for getting old cars off the roads.
Just as an observation from outside the States we don't have an auto manufacturing industry here in Ireland, all cars are imported, but you do have one in the USA. With that in mind while the country is under threat from economic stresses it's my belief that for the next three to five years you guys should actually put patriotism to the forefront and Buy American. Protect jobs. Keep American money in the American economy. Advocates of Free Trade will probably be aghast to hear me say that, but to hell with them, I don't hear much about them offering people jobs.
JF Kennedy said "Ask not what your country can do for you, but what you can do for your country". Granted he was a Democrat, so a lot of bodies on here might dismiss his remark just because of that fact.
When the chips are down, true patriotism is about supporting your country and supporting your fellow Americans, not about how good you are at field stripping an AR-15!
Buy American.
Joe