Honestly much like a lot of home improvement labor trades the cost will fluctuate based on how much business they're getting. That said if you are feeling scrappy to do it yourself that is actually a very doable option with micro-inverters and can save you can save a boatload of cash, hell you could just do all the physical labor and call in an electrician to wire everything up if that part scares you, but you have to be willing to do your homework and shop around, online you're not going to Home Depot to pick this stuff up.
When I got mine the base cost was $23k or so, which if I did it myself could have knocked that down into the $6-8k range easily, but San Francisco had a ton of incentives going off at the time which knocked $11,000 off the cost for the neighborhood I live in, and the fact I hired a company using labor from SF, then there was another $3-5k from PG&E (state of California), can't remember the exact amount, and then 30% from the feds in the form of tax credits, which luckily for me was off the base amount before the SF rebate, now it doesn't matter that I didn't own that in taxes that year, because I'm allowed to roll it over to the next year until it's all used up. Out of pocket money, the check I write was somewhere in the neighborhood of $10k, after all the tax credits and what not I end up paying a bit over $3k for 3.26kW of solar power, and at $1/watt installed by a professional... needless to say I had no desire to DIY and haul that crap to my roof. But I was in a very unique situation at the time that no longer exists.
