Mics for less than $100 will be very hard to come by. For open taping in festivals and the like, you may want to look into a pair of AKG C1000 or Studio Projects C4 mics. See if you can get them used from this board or from another board to save some money. You are still probably looking at over $100 for mics.
For tripods and the like, most tapers use the Bogen / Manfrotto lighting stands. You can get one from any of the major taping gear retailers, or maybe Guitar Center or somewhere like that will have one. You will also need a stereo bar so you can mount the mics and can attach them to the stand. The cheapest one is the AKG and this costs around $20 new from most of the taping gear retailers.
You also will need some mic cables that can go from your mics to the deck. I have no idea what kind of inputs the iRiver has so you may be building your own cables there. Some of the mic types have their own power supplies for phantom powering, some do not so you may also need some battery boxes as well (or you can build your own).
It may be easier at this point with a limited budget to get a pair of Giant Squid, Core Sound, or Sound Professionals binaural mini-mics and use those at the festival. Since it is outdoor taping, the omni issue is fine and you won't have to mess with a stand, cables, power supplies, and a bunch of other stuff if you are on a budget.