First and foremost I was wondering if there is one single budget microphone that is to acoustic recording what the Shure Sm57 is to electric recording.

Also, I was hoping if someone could explain acoustic pickups to me.  Say I got an L-03 and in a couple of years wanted to start playing some gigs that needed micing.  How would a pickup be installed and would it sound good?  Or will micing always work for gigs?

the 57 will work fine for acoustic recording.....you may do a bit better with a budget condensor like an Oktava MK-319, or for a little more, an AKG C1000S, but then you will need phantom power if you don't have it already.
As far as miking and pickups.   Miking is fine by itself if you aren't in a setting that requires higher volume levels, especially if you are a strummer.   If you are playing fingerstyle it really helps to have an internal pickup of some kind (my hands down choice is the Baggs I-beam) so you can bring the level up for those tunes.  I use the passive version of the I-beams (less wiring inside the instrument) with a Baggs Gigpro preamp for extra adjustability.

What if I do some fingerpicking, some flatpicking, and some thumbpicking?   :ph34r:

Also, how much would I be looking for the pickup/installation?

I'd definitely go with a combination of pickup and mic.......the Baggs that I was speaking of are approx 89 for the pickup and about the same for the preamp.   Most shops will install them for about 40.00.  You can do it yourself, but I've always had it done professionally.  I don't like reaming the endpin hole myself.

Check out the MXL 603.  It's the best budget mic I've heard on acoustics.

errrrr I will go with the LR baggs pickup for L-03 active ribbon transducer.....I was using it .....