My estimates show about 5 hours for the assembly time, so unless you get paid $1000/hour, this is not going to cost that much =) As for the time invested in software and hardware development - yep, it takes time, like any project is going to.
Answering to your "GSM not open" comment - yes, the GSM baseband itself is not open-source, and I won't be able to change that alone - I have neither skills nor time. My plan is to make all the other parts of the phone open-source, so that when an open-source baseband appears, there's a platform to attach it to.
It's a mighty goal and you're probably more than capable developer but even bigger organizations have failed to produce working phone sw stacks while leveraging open source components.
Therefore while it's a great tinkering project I'm really sceptical about the actual value this could have for "end users" unless the value is the tinkering itself ;-)
+1 for this. A GSM/3G/LTE stack isn't something you can write in an afternoon. I'm on such a project for my company for several months now and I'm probably still a year away from just being able to push a single IP packet through it.
That's why I won't be doing it myself - I'm just going to provide the platform, there are already people working on an open-source baseband, and they're much smarter than me =)
50$ for parts and 5000$ for your time. Oh well.. I'm sure some nerds will be excited ;-)