I make custom css' I find it fun and it's a good waste of my time. So I have a question for you. Would you be willing to buy a custom css that is custom made? How much would you pay for it? And finally is this a common service?
An example of my work are below: [click here]
Subetan OC Info
It is a common service, since there are so many people offering profiles Css boards are a little harder to find but it is indeed in demand.
Price is really based on the artist, if you'd prefer a starting point based solely on the look you can visit the Price suggestion board for estimates.
A good way to start is to offer freebies in the Profiles and Graphics Market. You'll get a nice lump of examples/practice/and possible future commissioners. Good luck selling :)

Pretty much everything that ReveL said. ^_^
Also, maybe try to... spice it up a bit? People love textures, you don't even have to do brushes. Fonts are always nice. And it looks like the navigation is a tag hard to read. Maybe try a background or something? Either way, coding spiffs are awesome swoonage around Subeta.
As for would people buy them? I personally don't because it's hard to find something I like. BUT. A lot of people love them.
Prices? Well, I only know from personal experience. When I was selling mine --> 1/2/3 <-- I got around 1.5 mill sometimes even two. It all depends on the buyer. And it's usually best to start around 1 mill 'minimum'. If people like it enough to pay higher--they'll tip.
Good luck with your CSS. It's fun, but the coding always gets me. ;^;