The problem with using Lulu's generic cover art is that there will be hundreds (if not thousands) of other books with exactly the same cover as yours...which really negates the whole purpose of a book cover.
You might try deviantart.com, where you will find a lot of artists offering really nice art for free or for a very small fee. There are also a great many places online where you can find high-quality, copyright-free art and photos. Here is a list of US government sources, which I have always found to be a real gold mine: http://www.usa.gov/Topics/Graphics.shtml
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I understand where you're coming from, but my cover won't stay generic. I've learned how to personalize a standard image and make it my own. As to paying for art - I just don't have the funds for that. Really.
This isn't quite an answer to your question, but I'm an illustration student with design experience looking for freelance work. I am also a good source for cheap cover art, if you're still looking around. I don't have a formal portfolio yet but I can send you a sample of styles I'm exploring if you're interested.