Keep in mind that prices of the American made G&Ls can vary a lot within the same model based on options, and used they generally go for about $800 + or -. Imported versions, i.e. Tributes, go for about $700 new and around $4-500 used.
Newer American made SBs are the typical P, P/J configuration while older models have what look like single coil MFDs. On the newer ones (as you've described) the SB-1 is a killer P-bass with volume/tone. SB2s typically have a pair of volume controls and no tone; many consider the bridge pickup to be more a part of the tone circuit rather than as a stand alone design (naturally opinions vary)-- and some are delivered with a factory tone control option.
What makes the SB different than the LB? SBs have the MFD pickups and narrower bodies than the LB. Tone wise, I find the SB can nail the LB (or traditional P-bass) tones, while giving you even more tonal flexibility than the traditional split-coil pickup.
Outside the details, the SB is a fantastic P-bass, featuring the same level of excellent quality as others in the G&L line. When looking to buy any G&L be sure to consider the type of neck you like (wide, narrow, quarter sawn, flat sawn, etc.), and go from there.
Happy hunting!
P.S. if weight is a concern, keep an eye out for "Empress wood." It can be found as an option on newer basses
