Here is something that you may consider trying.
I sound proofed my car by using a spray on bedliner. The cost was around $175 but It was way cheaper than using dynamat which was around $400, although i'm not sure how much bedliners are now as i did this 5 years ago.
The drawback of this is that you have to have a shop with an aircompressor. You can rent a spray gun from lordco and purchase the sprayon bedliner from them, they may rent the compressor too. If you are going to do this you have to remove the interior and wipe down everything with a degreaser or it willnot stick. When this stuff dries it doesn't smell and it's not sticky like undercoating, it is a rubber compound and is very durable and lightweight.
Warning be very carefull when spraying this stuff is very hard to remove, spray in even coats about 2 . Make sure to let it dry for a day or so, after if you really want you can put some pink insulating foam inbetween the panels and the body. And If you are really nutz like me youe can purchase doublesided molding tape to put in between each and every plastic panels that touch.
After all is said and done it only adds about 10-15 pounds and is cheaper than dynamat, although dynamat is much easier to apply.
Now the bedliner alone will make a drastic change in the road noise but if you add the insulating foam it will virtualy eliminate it. I am by no means a veteran on this forum but i have been around the Dsm scene since 1995, just never part of bcdsm. I have done this to a few of my friends cars and it worked out great, i hope this info will be a help to you on your journey for the sound proofed car.
Good luck!
pm me if you need some more info. :?