Okay so sounds like you have/want...

Home Theater with typical sources AVR or separates & a few lighting loads with at least 1 keypad to control them.

8 zones of audio with a Sonos or similar for streaming music.

3 in-wall locations for controlling audio and subsystems (pool/security & might as well do HVAC)

This is definitely an in-the-box control4 system. Here are a couple of things to think about in terms of cost difference.

1. If the Pad8a is working i think you can continue using it with 3 Series processors. Dont quote me on that :)

2. If you stick with Crestron you don't need to replace the lighting hardware you already have.

You would need to buy: (assuming the PAD8A can stay)

1 MC3 Processor
3 In-wall Touchpanels (or a mix of touchpanels and keypads to lower cost)
1 Wired lighting keypad if you can get cresnet wire to it or a wireless keypad
1 Autonomics Mirage MMS-2A

With hardware and programming and labor i think you are looking at a $15-20k Crestron upgrade assuming you have wire everywhere or can get wire everywhere and there are no surprises. A firm with their act together should need a day for discovery, a day to pull any wire and remove old hardware, 2 days for installation and 2 days to configure and load/test programming. I have a big jump there ($5000) because i don't know how much work it will actually take to do the installation. They may only spend 1 day doing discover and rewiring. They may need to have 2 guys on site for programming & testing. Who knows. Doesn't hurt to get quotes from two companies.