I didn't even know of the negative criticism (though I'd assumed there would be some) towards the project when I attempted to reach out to Jeri Ellsworth and get some input. Looking for any contact info I came upon her Twitter account and her tweets mocking the project and calling it a scam. I do admire Jeri and look up to her so those tweets were crushing to say the least. A little more research lead me to this site and this forum post. Reading it didn't life my spirits either.
Don't take it personal. Engineers are not politicians and they say what they think.
Some red flags in your campaign were "I don't have the technical skills" and you didn't demonstrate in your campaign that you have done some research how much it costs to hire a company to do it for you, just wishing it should cost $75. I guess only recreating the old keyboard would cost 5 digits in tooling and design cost. And if you don't sell at least thousands of it, the price of each one will be too much to be in the limit for your desired system price.
Another point is the hardware compatibility. "Being able to use peripherals built for the machine" would make it even more costly, because just trying to 100% implement the behavior of the expansion port of this old computer is a mess.
Finally a 100% backward compatible C64 would be very difficult, with the VIC as the most difficult part. The best implementation I know so far is used in the Turbo Chameleon, and just the module, without keyboard or docking station, costs EUR 200. Take a look at their mailing list and read about the problems they have, and they are developing it for at least 5 years now (this is when the Yahoo group was created). For the C64 DTV they just patched the bundled games until they worked
That said, with a Raspberry Pi it might be possible to create a cheap solution, of course, not external hardware compatibility, but most people want to run the software only anyway. I've tested it a year ago:
http://www.raspberrypi.org/phpBB3/viewtopic.php?p=148184 and someone has created a full C64 with it:
http://retrotext.blogspot.de/2012/06/its-complete-post-is-coming-soon.html I would recommend that you try to rebuild this, because this would help you to understand some of the problems that arise when you try to build something more difficult. The blog entry is very detailed and should be no problem. You don't have to use a working C64 for the keyboard, buy a broken one from eBay.
When you have a working prototype, you could ask manufactures for the keyboard and the case, and the Raspberry Pi foundation if they can deliver you the required many Raspis. Then start a new foundraising, if you have all the numbers, and don't use a flexible goal, because you can't pay the tooling and other setup costs from it. Maybe even easier would be to use a PC keyboard (you don't need that often the keyboard for gaming on the C64) and some laser cutted parts for the case. This would reduce the required number of units to make it cheap.