The two most often suggested "budget" condensors are the Marshall v67G and the Studio Projects B1.
Start with those. However, I'd stray from using only one microphone for "everything", especially it being a large diaphram condensor. Mic choices are dependant on the type of sound source, and the desired sound. Budget is a big factor.
Miking guitar amps (assuming that's what you meant by "guitar") is traditionally done with a dynamic microphone (i.e, Shure SM57) to capture the "meat" of electric guitar tones. But it's not uncommon, especially with pop and blues artists, to stick a condensor 12 inches from the amp mesh, and let that be the sole microphone for guitar tracking.
Acquiring your desired sound requires experimentation with microphones, mic positioning, and pre-amp selection. Most of the time, just
one microphone won't cut it. Each microphone accentuates varying frequencies differently, and converts sound into electricity differently, and so different microphones do not sound the same. That's why recording engineers purchase more than one for their studios.
With everything, see if you can "try it" before you buy it. Search the board for suggestions on micing particular sound sources, and achieving desired tonal variations.
A decent mic purchasing guide can be found here:
http://hr-faq.org/
Good luck.