So you have some pieces broken free from around the radio area of your dashboard?
That blows!
If I was going to repair the dash, I'd find a sturdy material that I could cut easily, to use as a backing reinforcement.
Like maybe some aluminum strips, or some thin plastic sheets or something (depends on how large the broken pieces are).
I'd cut some pieces that will "bridge" the broken sections and glue half of a strip/sheet to the good side of the dash (on the backside, and placed so that it hangs out into the missing piece area) and then use that to hold and glue the broken piece/pieces to.
I think edge gluing that thing back together would be very difficult to try because glue joints are not generally as strong as the original material.
That's my best suggestion, since this method doesn't rely on gluing the broken edges together directly for its strength.
It will look cleaner at the joints too because you won't have squeeze-out to deal with, or if you do, you won't be afraid to wipe it all away for fear of compromising the glue joint.
As far as what glue to use... I've had varied results from many different types, but I'd probably go with a two-part epoxy. I myself would go with one that has a little longer cure time because 5-minute epoxy sets up too fast for me.
10-15 minute gives you more time to work.
Hope that helps.
I'd hope even more that you could find a cheap replacement.