I suspect the practical answers have already been given. From here, it's a matter of deciding if you want to buy or DIY traps. The first sticky under the Bass traps section is very helpful.
For DIY, look around for an insulation supplier in your area and see what prices they have on insulation and mineral wool.
Going to be a bit of a hassle to move traps around to get the car in and out. So you'll want to keep that in mind as you think about how you're going to make it all work. The traps are going to eat into your garage floor space. I used to have a garage where I couldn't lose any floor space and still get the car door open.