You can do so much SEO on that site yet. As some others already said, you don't need a mentor just keep on learning SEO and implement it...
Here's a quick list of things you should put a good amount of work into.
1. URL's - rewrite them as others said
2. Title's - get specific! Currently they're just dynamic but you want to catch longtail searches. So for example for this listing:
http://www.driverchange.com/UsedCarD....aspx?Id=81637 the title should be "User car: 1996 Bentley Brooklands,NY Brooklyn - Cars for sale"
3. Remove meta-keywords they'll just end up harming you. Make your meta-description much more specific e.g. include specifications for cars, or else dump meta-descriptions since they can hurt you too.
4. Don't link you pictures directly. Put them on pages or create a nice little script that changes the big picture when clicking the small ones. And add an alt-text to your image which is specific to the listing. Image search can bring decent traffic to a site like your.
5. You don't link enough internally. On the pages for a specific car listing you should link to at least 10 - 15 related listings.
6. Build links from other sites. And make them point directly at specific categories. On a site as big as your all link popularity will "get lost" on the way to the actual listing pages.
7. Adjust the photo sizes server side. You're just changing the size with html with makes you website very slow for people. So make image files with the actually used sizes and compress them a bit more.
That was what I had time to come up with in 5 minutes, so just get to work. Learn more SEO and implement. Afterwards get back to forums and ask for advice again.
I'm sure your site can do very well.
Btw. consider that you site is almost brand new. You need to work a lot on building links - quality links from "trusted" sites. That will have a big impact and you rankings and traffic from especially Google.