What is the cheapest available MacBook Pro I "need" to record acoustic guitar, piano, and vocals with minimal effects?

I’ve decided to invest in a MacBook Pro for music recording – it is a very simple set-up, with a dual-input interface for my guitar, piano, and microphone. I am willing to spend whatever is necessary for the best possible recording quality (as I intend to record my demo using the MBP) but I don’t want to buy more than I need. I am trying to figure out what size, and how much RAM, processor speed, memory, etc. I will not be needing drum loops or anything like that – just laying down organically-recorded tracks and then mixing everything together. Thanks in advance.