To give a rough idea of the price range (in US dollars) to get excellent audio recordings, some models such as a  20$ USB logitech wand mic can produce quite good results. 50$ could step you up into something that sounds fuller, 80$ to 150$ can get outstanding results in combination with good recording process. 

recommended models
for audio-tipitaka purposes

NOT recommended models  for audio-tipitaka purposes

Here are some resources  that discuss pros and cons of various mic's

librivox microphone showdown (mp3 samples for many brands of mic's)

forum.librivox proposal to do another microphone showdown

microphone dedicated forum suggestion