My extra array that we just added was $1.40/watt for another 3kw array or SolarWorld panels
That's racking, inverter, etc.
If you do DIY, you'll win..
Depends how much you get paid at work I guess if you need to take any time off to get this job done. Yes you can work on weekends sure, but how long will it take for a rookie to install a non-trivial size array? And it is not a 1-man job, so you need someone to help you too. Then you pay an electrician, pay to get all the permits, and deal with your utility company to get a PTO. Because of these reasons I'm working with an installer, yes my payback period will be 2-3 years longer and I won't be as proud of myself with no right to brag about the DIY route, but I can live with that.
'11 SL, totaled
-1CB@33k/21mo, -2CB@53k/33mo, -3CB@68k/41mo, -4CB(41.5AHr)@79k/49mo, -5CB(38.85AHr)@87.5k/54mo
51.1AHr, SOH 80%, 150k miles