Hi,
I am able to help you with your project. I am a native English speaker / writer with transcription experience. I have fast (75wpm), accurate typing and pay great attention to detail.
You haven't mentioned anything about the content or length of your audio, so my proposal bid is a guess. If you pm me with further information, I will be able to quote appropriately.
As a general rule, 1 hour of audio = 4 to 5 hours of transcription, depending on the number of speakers, quality of audio, background noise, clarity of accents and format. For your budget of $250, I can transcribe up to 4 hours of lectures / seminars, or 3.5 hours of interviews.
Please feel free to contact me if you have any queries regarding this proposal.