I've built several racks that were cheap --errr-- inexpensive. This is probably the one that would suit you best:

http://paddleandoar.com/notebook/orion/img_seatrials/med/kayak-launch1-med.jpg

Because there are no rain gutters I had to open the doors and screw on sheet metal tabs about 1" x 3". No drilling necessary as there were screws holding on the trim already. I used galvanized steel - don't use aluminum! They are strategically bent so that the doors close and then they wrap up over the top of the car.

The cross bar assembly sets on the roof and turn buckles attach them to the tabs. Perhaps larger foot pads would be wise to protect the top of the car. The cradles for the boat are foam glued to wood. Although these have bolts that go through the cross bars you could as well have wooden blocks that attach to the cradles and come down - one in front and one in back - of the crossbar. Once your kayak is strapped to the cross bars they won't go anywhere.

This is a bit involved, but it is cheap!

PaulMon