By e-book readers,do u mean the one meant exclusively for that like the amazon kindle,sony reader etc which have e-ink technology(in short,looks similar to while reading on a book,no brightness) or the ones u can also use for viewing books.(like any pda or video player with 3" or above screen size).
AFAIK,the sony reader costs a lot.(250$ upward) & amazon kindle even more ( 400$ upward).
PS:If anyone knows a cheap e-book reader ( should be able to read books properly,no e-ink etc required,please do tell).