When do you "bite the bullet" and get something to at least start shooting with?
If good glass is forever, why do people sell?
people often sell lenses when they're upgrading... some of us arent collectors i guess.
i started off cheap too with a sigma 18-200 as an all rounder and it performed well, but i found for shooting cars the two best lenses i have would be my sigma 10-20 wide angle (which cost me about $600 back int he day - needless to say it just might be a little cheaper now) and the 50mm 1.8 which set me back a little over a $100 but well worth every penny.
so when we need to make a start i'd recommend the 50mm for sure. its sharp, cheap and ridiculously light weight. definitely a good place to start especially in the 200 range. i can vouch for most 50mm owners that its definitely a great lens for cars, portraits and pretty much most things.

