The extender kit you mentioned is the Q stretch kit, which sells for $60 on ebay. Thule or Yakima sells these extension kits. Research yakima.com or thule.com, find what length cross bars and clips you need. Craigslist search, ebay search for used sets. The used kits will run you around $150-$275. The link i provided earlier has a guy selling the cross bars and towers for $150, all you need is the correct clips and the extender kit.

The simple foam blocks works but its going to be a bit hard to unload/load the kayak if you're doing it by yourself (without scratching your car's roof).

Hope this helps you decide. I say buy the kayak first so it will motivate you to get the roof rack. :D

Using any foam or air pads that sit on the roof are going to be a big risk of scratching or scuffing the paint finish due to dust, dirt or sand getting between the pad and the paint. The better option is to get a rack that mount to the body at door openings or gutters. Also the pads might put pressure on the roof that could dent in the center area of the roof. Body or paint damage would lower the value of the car or cost more to repair than buying a rack that can better support the weight.

http://img.photobucket.com/albums/v2...pswaqypg1i.jpg

im using foam blocks and they work great for my car but i use my ezwheels to load my kayak. you'd be better off getting a real rack but if you want something in the mean time to work and for cheap