"300~450?"
Other folks will recommend Apogee products, but I'd suggest you look elsewhere. They are high-buck and may limit your input options.
With a $300-450 budget, you have to consider that you'll need:
1. audio interface
2. at least 1 mic
3. mic stand, cable, etc.
IMPORTANT QUESTION:
Do you want to record both vocal and guitar "live" (both at the same time), or do you want to multitrack (that is, record guitar first, then voice, etc.)?
You need an interface with at least two XLR inputs (and the XLR inputs should also offer "direct" input of the guitar if you wish to "plug right in" that way).
For a USB-based interface, the Presonus "AudioBox" might be a decent way to get started. Try doing a google search on it. If you don't already have a mic, stand, cable, etc., there are some halfway-decent "bundles" out there, such as:
http://www.musiciansfriend.com/pro-audio/presonus-audiobox-usb-recording-package?src=3WWRWXGP
If you want a firewire based interface, I think you'll need the USB-to-firewire adapter for the Retina MacBookPro (it doesn't have built in firewire, is that correct?).
If I was looking for a firewire-based interface, I might be considering this one:
http://tinyurl.com/9thllwc
Finding a good mic is a journey in itself. Beyond this forum, you might also do some searching at gearslutz.com.
One of the "sleeper" mics out there is the MCA "SP1":
http://www.google.com/search?client=safari&rls=en&q=mca+sp1+microphone&ie=UTF-8&oe=UTF-8
I don't have one, but others who do (including folks over at rec.audio.pro) suggest it offers performance that far excels any other mic in its price range. And it can be modified to make it sound very much like a high-end Nuemann....