It is quite understandable that you are looking for cheap transcription services. These services can run up a huge bill if you have a large audio file to be transcribed. At the same time, it should also be remembered that if any company is offering dirt cheap prices, then either it is a purely charitable organization which is highly doubtful or the quality of their services are also as low as their price!
Does this mean that you will need to pay through your nose every time you get an audio transcribed?
First of all; be wary of those companies who have a fixed rate for all their projects. Choose a company that will first review your uploaded file and then give you a quote; something like how Hour Trans does. Rates should depend on not only the quantity of work but also the type of work and the time it will consume.
Now, at times one may need to get urgent transcriptions done too for any number of reasons; you would want to be sure that you are not ripped off because of your desperate situation. You can always upload your files on multiple websites and get a quote. This will ensure that you are availing the most reasonable price.
Next, accuracy is of paramount importance. So avail of any trial offers first to judge this aspect. If documents are of any legal or medical nature, then errors can prove to be very costly. Of course the same is true of other fields such as academic, business etc.