the thing you print is that hard or flexible?
And is it possible to print a phone protector?
In my opinion a phone case would be best printed in PLA as it is tough but slightly flexible. Lots of examples here
http://www.thingiverse.com/search?q=phone+case&sa=To be honest this wouldn't be the cheapest phone case as they are normally mass produced.
But from a rough calculation based on the following case
http://www.thingiverse.com/thing:72542 I would print this for £10 plus £3P+P (royal mail recorded delivery) so 0.033
BTC (rough napkin conversion).
Any questions please let me know.
Thanks
Trilby
Edit: I am actually printing that phone case as I rather like the design will post some pictures tomorrow of it.