2 domains, 1 content

Hello!

I have a question/problem that I've been trying to find answer for last 3 months and never got what i'm looking for. Maybe you can help.

Situation

I'm running main WordPress blog/site. It has 800 posts with images. I want to make other blog using subdomain, which would be using another theme and another design, but the post would be the same on both sites. I know that it's easy to export and import posts (with images), but I want then to aoutmatically appear on the second site with images, categories, etc when published to main site. Someone told me it can be done with RSS feed, however it does not include full posts and images, and even not all posts. Also, those plugins that allow to to that, are expensive and I don't have any resouces to to it. Meaning, I need to to it using 0 money. Since WordPress is so popular, it must be possible to pull it off somehow. Isn't it?

Also, sorrt for my bad English.

Greetings,
Andri