Some online retailers I like include

blueskycycling, pricepoint, huck and roll, jenson and nashbar. You can also check around for bike clubs in your area. There may be people with used parts that they will let you experiment with. That way you can get an idea of what works and not. Putting a 9 or 10 speed on a '06 might run into some problems, maybe not. Tweaking bikes is part of the fun in the game. Enjoy it. Wish I could be more help. Best I can say is get the rear cassette, Rear D and shifter all at once. Match the eqt as close as you can.