I doubt 1 page website, no matter how unique, would sell for $30 Let's assume it doesn't have any links, PR or traffic.
It not depends on how much of content.It depends on quality of content and on how much visitors are visiting your website.
it depends on the quality of the content. quantity of non-relevant content cause any increase in value. good content should contain enough iformation for the site visitors. The content should be direct and serve his purpose, too long written texts discourage the reader.
It needs to be unique and it need to have atleast 100 unique views per day. Also in my case page should have some earning- no big, but atleast some cents. But thats just my point of view. Good luck.
You should focus on quality and optimized content to make it work for you. Proper usage and placement of keywords and using semantic versions of your keyword phrases adds value to your content. By the way, regarding the price (of $30); even if a website has only a single page with unique content, it can be sold for much better amount than $30. Good luck,