[Note that I'm rather new to all this so don't speak with that much experience, or authority..]
I bought an Apogee Mic for £50 second hand and an Apogee Jam for the guitar for £30 also second hand, I use these with an iPad2 and an ancient iPod touch (4th gen) on which I have the Garageband app.
The good thing about the Mic and the Jam is that they have built in pre-amps, do the digital conversion and connect via the 30pin digital input not the headphone jack, also they don't need external power.
I think the quality is excellent, but if you're interested there's plenty of reviews and samples out there.
The portability is perfect, the battery life is a limiting factor though.
This is what persuaded me to try this option;
https://soundcloud.com/apogeedigital/willie-k-recording-ukulele-and Garageband is fun, cheap, easy to use has been great for me as a beginner. Although the version on my iPod (maybe IOS 6?) is very basic and flawed - but then most apps don't have any backward compatibility at all, certainly no that far...