First of all.., I just want to say.., on behalf of all men out there.., that what you're doing is very sweet and thoughtful.., it warms my heart to know that there are girls out there that take so much effort and put so much thought into gifts for their boyfriends..
Now.., you don't have to go all-out.., here is my suggestion since he likes the guitar.., instead of getting him a real guitar.. (a personal choice).., you can get him something more valuable and throughful.. (motivation to learn the guitar).., that's right.., you can get him guitar books.. go on Amazon.com and find some.., believe me.. he'll definitely appreciate the thought behind it.., especially with a well-writen card..
Best,
GrkScorp
If you can't stop the Wind, then you can't stop the Storm.