The standard belief is your book cover draws the reader in and your back cover makes the sale. Most book sales, however, are not made in brick-and-mortar stores any more. But while the kind of cover you require for your book depends upon many factors (including “Where and to whom are you selling it?”), it’s still the best idea to put your best foot forward when it comes to cover design.
Ideally, you want to appeal to everyone, but the reality is the self-published author may need to cut back on certain design aspects on a first title. Cover design is one you should not cutback on, however, if you can’t spend money, spend some time investigating the hows, whats and whys.
There are many places where one can get royalty free art or photography which may be used on a cover. One of my favorites is: http://www.sxc.hu. Be careful to read and abide by the usage conditions which are typically quite liberal. Most allow for use on the covers of books, but make certain that is the case by reading the conditions. It’s always good business practice to credit the photographer, too.
There are myriad places where you can find low-cost book cover design or cover art help. Elance.com is but one. You do get what you pay for, but not all self-publishers can afford to pay for everything they need.
If you have a good artistic eye (or if you have a friend with a good artistic eye), and use a template available from one of the print-on-demand companies, a royalty free photo, and some persistence, you may arrive at acceptable results for your book cover. Remember to always abide by all the technical requirements for every market you’re after. Book stores require certain trim sizes while Amazon does not. Research, research.