Need advice on creating a 3x3x1 inch, 5-sided open box with low thermal expansion.

Current box is machined aluminum and meets all of the specifications below but expands to much for the temp range.
The temperture range is -20 to 30 deg C.
The missing side is a 3x3 inch top.
Box needs to be strong enough to with stand a man walking on it.
Box needs to be very flat.
Need to be able to produce box affordably, must be under $200 in quanitys of 100. Under $100s would be even better!
I'm out of my area of expertise so I hope I've supplied the right parameters. Let me know if more data is needed.
Thanks in advance!
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temperture -> temperature with stand -> withstand quanitys -> quantities data is -> data are
What are you a'trying to do, recreate a David Blainish trick?
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Thanks "alot" Autymn, I stand erected. :-)
But seriously, thanks for bumping this thread up, any real help would be much appreciated.
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You didn't answer me.
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Autymn - No, I'm hoping to sell this to the "David Blainish"es of the world. :-)
Once again, thanks for bumping this thread up, any real help would be much appreciated.
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