Hello,
We are interested in developing a website similar to Cardomain.com, where car enthusiasts can show off their cars, with pictures, profiles, diaries, etc., and I wanted to get recommendations on what web software platforms might work well for this? Preferably Open Source or something affordable. Would greatly appreciate your help and opinions! 
I have had a look at Cardomain.com and do not believe that it is using any thing that can be got of the shelf.
Clearly always dangers with allowing Joe Public to upload content to your site. So please be careful.
Might something along the lines of a Wiki sufice?
Basically if you want to make such kind of website then you should hire web development company. But if you want to make it yourself then you can go with wordpress.com which is best platform to get ready made plugins and themes.
There was a specific requirement for
car enthusiasts can show off their cars, with pictures, profiles, diaries, etc.
This isn’t something that Wordpress would normally be used for. Do you believe that a Plugin exists even for this?
Thanks for the replies so far everyone. Yeah, I’m sure Cardomain.com is using something completely custom. But basically what I’m trying to determine is if it would be best to hire a web dev company to build something completely custom for us, or if there is some existing platform, such as Wordpress (or something else) that would work as a good base and could be modified to our needs or would have plug-ins or themes that would work.
As I mentioned earlier might Wiki software provide the sort of functionality you desired. A sort of collaborative knowledge base of cars allowing picture content.
Could Wiki software be modified to have a user feel and functionality similar to cardomain.com? And any recommendations on any particular wiki software?
Almost impossible to answer your question on this forum. You would really need to outline your goals, aspirations, and budget.
cardomain.com has been built specifically and somebody has either used their own time and expertise to make it or has invested good money in having it done.
If you do not have a computer background consult with somebody who does. If they are real professionals then they will not only point you in the right direction but will give use a proper route for achieving your objectives.
If your aim is a cardomain.com site of your own then a wiki will not do it for you.
Good luck with your enterprise.
Like a few other people have said, wordpress is a very good choice either from .com or on your own server on .org