I got a 100' X 20" roll off ebay for I think $60 or so (shipped) It would have been enough but I screwed up on probably 5 or so windows & had to run the store & buy another small roll to finish up 2 windows in the back.
Heres a good tip, measure your windows height before you order. Mine are 10.5" (each piece) so 20" width wasn’t wide enough to cover the top & bottom & I ended up with a lot of scrap. I think a 50'X24"roll would have worked out better for me. Also it's a good idea to do the tinting before you build stuff thats going to be in your way.
I did mine at 20% because I thought any less would block out too much light in the daytime. I'm happy with it, during the day it's hard to see inside & if its sunny out its almost impossible to see in.
Here's an ebay link to a 100'X24" 5% tint from the same guy that I bought mine from. Looks like it'd be $70 shipped. Click to see his other auctions, he always has a lot of tint on ebay.
http://cgi.ebay.com/ebaymotors/PROFESSI ... 4692QQrdZ1
There’s another post on here about window tinting check it out.