I've been listening some binaural recordings for the last couple of weeks and it got me interested. Browsing the internet for information on mics I landed on the Sennheiser Ambeo Smart Headset which seem to be discounted at 50€ at the moment.
It seems like it works with iOS devices only, but since Bietfriek mentioned the iOS apps I guess this could also be an option, and for that price I'm considering getting a pair myself. I'm not sure what are the advantages of using a recording device instead of a smartphone with this kind of mics, maybe I'm missing something but this seems like a good place to start experimenting with field recording.