If you are considering photographing wedding's professionally, but you don't want to spend $1500 on a lens, you should reconsider your plans.
It takes a minimum of $10,000 worth of equipment to shoot a wedding professionally. If you don't have it, you just aren't ready.
If you show up with one lens and one camera you pretty much have a 100% chance of fracking up their wedding. You are going to get a reputation as someone who is not professional, and after 4 or 5 weddings, word will spread, and you will never be able to get another client again.
Edit:
I am not saying you should give up. I am saying you are not ready. If you can't afford $10k in camera gear you should save up until you can before you consider shooting weddings professionally.
How would you respond to me, if I told you I wanted to open a restaurant, but I only had $500. You would tell me it was impossible and that wouldn't even be enough to rent the building let alone hire staff and buy ingredients. And you would be right.
If you insist on showing up to shoot a wedding without the adequate back up equipment, and your gear fails, you can expect to be sued. Here is a video of a "professional" wedding photographer who shot a wedding without the proper equipment and got sued.
http://www.youtube.com/watch?v=RjBSIvg3pjc
P.S. Thanks for the very long email that you sent me. Sorry, but I have only been shooting weddings for a hair over 10 years, but it appears like you know a lot more about wedding photography than I do.