One of the problems that I've had with lowest bidder translations is that the cost of a poor translation can be quite high. Working on a large real estate management application a few years ago, we hired a firm based on cost alone for a bunch of translations; and they did some weird things like using the word for "zipper" when we wanted "zip code". The translations were generally correct, but little things like that really made us look pretty bad in the eyes of our international customers.
So, my point is that I would go out and look for a company that had a good translation track record before trusting the public face of my company to someone on the basis of cost.