My only experience is of working with co-publishers who arrange the translations themselves.
I know that it's costly to employ a good interpreter, and that if you skimp the resulting text is unlikely to be effective: it's not just a question of interpreting the words you've written and getting the grammar straight, your interpreter has to also echo your voice, the rhythms of your speech, the tone of your novel. This is very hard to do effectively.
I've seen some self-published writers use things like Google Translate to translate their books into other languages. It's really not good. Make sure you do it right, or not at all.
A few hints: use translators who move work from a foreign language into their own first language, as you'll get a more authentic voice that way; use translators who have already translated several books, which have been successful; and make sure you get everything you need translated--the book, the title, the blurb, and so on.