I haven't taken any ECE exams, but I too share the insecurity of taking an exam without a guide. Another reason I've chosen some Dantes exams over ECE exams is the cost is less.
As an alternative, however, for those exams that absolutely must be taken maybe you can do a search on ebay or elsewhere for a study guide that another test-taker has created. I've found a few posted on ebay which, although I've yet to apply them, are very thorough. Just a suggestion...