If the interviews you are doing are all in a studio or room, you could hook a mic up to a laptop and record like a regular podcast using podcast software, or Audacity, or something similar.
Sony MiniDiscs used to be popular at one point, for recording audio on - never used one myself, and never saw a model with a digital connection either.
Regardless of how you do it, it's going to suck a lot when it's time to edit. You'll have to manually sync up the audio to the video. If you edit the video (to get rid of umms & errs), you'll need to do the same for the audio - not so bad if both video & audio have been running continuously, but realistically you'll be stopping & starting video & audio many times (and neither at exactly the same frame)