TEP is widely recognized as the best translation practice. Unfortunately, not all translation service providers follow the best practice. Many translation companies offer you "T-only" translation services, without editing and proofreading. Usually, E (editing) and P (proofreading) may take the same amount of time as T (translating), or even more. That's why some companies will add editing at your request but will charge you an additional fee for it. So, it's important to ask what their offers include before you compare their translation rates. Only an apple to apple comparison is meaningful, right?

The paragraph above also partially answers your question why translation quotes vary so much - it is because translation quotes are often for totally different service levels in spite of all being called "translation service". In conjunction with mentioning translation quotes, we would like to give you some easy ways to screen out the poor translation companies.