There are many Mac apps out there that will allow you to record. From the low end to the high end and in between!
If you are planning to do a bang up job you'll want a few mikes and even a few different types, as different instruments require different methods of recording. Most of this gear should be rentable.
All of these mikes plug into a digital to analog converter (DAC) to convert the analog to a digital signal. Each one is treated as a channel 4 or 8 channels should be enough for a small ensemble. Each of these channels feed into your computer and recorded independently. That way you can mix them together for the best recording. Making sure the louder instruments don't drownout the softer ones.