Most will say a system is only as good as the dealer and their ability to program the system. I have Control4 - the dealer did a poor job on the programming but I have hooked up with another dealer who is fixing all the problems and now I am enjoying the system much more.
Other than Crestron and Lutron you have Control4, Savant, RTI, URC, Elan and several others.
Most people will rave about the ones they own. Any of these can accomplish your goals of lighting, HVAC, audio and video distribution.
Sonos on Control4 is great, and Extra Vegetables just released an update to the driver to give you more functionality. For video distribution, some do it via a matrix and some put sources (cable boxes, apple tv or other wifi devices) local at each tv. Pros and cons to both set ups. Lighting - Control4 released new lighting this year which I have in my house. I have about 25 devices - a mix of dimmers, switches and multi button key pads. I got the engraved caps and they look sharp and function well.
My HVAC is controlled as well and its simple. I have sensors on the walls and my C4 thermostats are in the basement and I control everything via C4 interfaces (touch screens, remote control, phone app, etc)
Quotes will vary - if you the wiring is already done and you just need some hardware and programming, I think $25-$30k for Creston is likely a bit high but then again I've never priced Crestron hardware. What I should say is Crestron is one of the bigger more robust systems out there and they are programmed line by line for your house - so a lot of a quote has to do with programming hours. Systems like Control4 (and others) are more plug and play so they require less programming hours, but have some limitations with what they can control. That being said, 95% of residential installs are likely ok with any system from what I gather.
In the Control4 environment you still need a dealer to get started, but once up and running, you can do programming on your own - you just cannot add hardware on your own, you need your dealer for that.
Again, find a dealer you like and trust and you can see good work examples. Any of the systems I mentioned can accomplish your goals. I did not touch upon 100% DIY options as that is something I did not research when I made my decision.