I hlep put one in my friends galant. it was a pain because it didn't fit right. I don't know what type the window was for (ebay oem), looked like it would fit. We ended up making/welding a channel for it and flush fitting it in. the electronics weren't all that hard to wire up. $350 for labor is a bit high, are they quoting for a certain amount of hours or is that flate rate. installing one would probably take like 2 hours, its all about what tools you have on hand. I would look around and say what one shop quoted, you can baggen it down a bit.
Oh also you are probably going to want sto make a new headliner board. the s30 came with a headliner but it was contact cemented dirrectly to the underside of the roof.
edit: when did you see if the wheather stripping for the window had wheather sealer on it (glue) most people either forget about it or just don't care when they put it in themselves.