I found a nice used briefcase at a Goodwill store for $10.00. I bought some 1" and 1/2" foam padding at a fabric store. I also bought some stretchy fabric and some spray contact cement at Walmart. Not my choice of fabric color, but it was either that or lime green.
I stripped out the inside of the briefcase and cut 2 pieces of the 1" foam and 1 piece of the 1/2" to fit the bottom and top of the case. I then cut the middle out of the 1/2" foam to fit the outside of the MBP. I then glued the 1/2" foam over the bottom 1". I sprayed and glued the fabric over the foam pieces. After covering the foam with the fabric, I sprayed and glued the 1" foam to the top and other 1" with the 1/2 attached to the bottom of the case.
Total cost was under $25.00 and it was easy to convert from a briefcase to a Macbook Pro case.
It does a great job of protecting my MBP, and can be taken on the road without hunting up a case. Since I now use the case in the house, and not just in the truck, it pretty much stays in the case all the time.