HUGE difference in tint jobs, imo.
First and foremost you should find a reputable shop. There are a lot of crappy tint installers. Secondly, decide if you want hand-cut or machine-cut tint. There are benefits and drawbacks to both.
You're more likely to get a "good" install on machine cut because it dramatically reduces the minimum skill level required to make an acceptable install. Basically the installer lays out a sheet of tint and a enters your vehicle info into the computer. A computerized cutter, similar to making a vinyl sticker, will then cut out the shapes necessary for your vehicle. The downside to machine-cut vinyl is that you will be able to tell it's aftermarket tint when you roll down your windows. There will be a clear line around the edge of the top of your windows. When I was younger I was ticketed for tinting my front windows, and there cop used the fact he could feel the lip of the tint with his finger as evidence to ticket me.
With hand-cut tint, there's more room for the installer to screw up, but an experienced pro will give you a better result hand-cut than machine cut. It's the only way to get the tint to go edge-to-edge on roll-down windows.
Another big difference between a good tint shop and a bad one is how they handle the hard-to-reach areas like CHMSLs. Bad tint shops will cut around them. Good tint shops will do a little disassembly and tint the full glass.
Beyond installation quality, you've also got the tint film, itself, to consider. Inexpensive films are going to turn purple. Really cheap ones will turn purple in a year or two. They're also more likely to delaminate, and then you end up with purple film that is "bubbled". It doesn't matter what you drive, it'll instantly look like a hooptie. A quality film will remain grey and not purple, and the adhesive will last for decades. Cheaper tints are dyed, and those are most likely to go purple. Mid-grade tints are metallized and they do a better job, but they tend to weaken GPS and cell coverage. Ceramic tint is what I'd recommend.
As for brands, there's a lot out there. 3M is the lowest-quality I'd ever suggest. I've had good success with Johnson films -- the best installer I've used preferred Johnson. I've also had Llumar on several vehicles and it's worked well.
I would say that you can't shop just on price -- especially in SoCal. A bad shop could easily charge $350 and find enough suckers. Likewise, I've seen some great affordable shops, too. Also, "what" you're having done will affect the price. Just the front windows? All the glass?
I would absolutely avoid any "chain" businesses. Beyond that, you need to check their reviews, research the films they want to use, and ask questions -- choose who you like.