garrettwp let me try to address some of this
I also started from Xbee and posted here one example. But yes Xbee is to expensive and I think too complex.
I’m using aliexpress for about 3 years. Sure you need to count on a seller reputation like you should do everywhere. I had just a few not significant cases and in 80% of them I able to agree with the seller on resolution before opening a formal case. On other 20% I win through ecrow case procedure.
maniacbug the author of RF24 we are using here has experimented a lot http://maniacbug.wordpress.com/2012/03/30/rf24network/
Before I purchase a Replicator 2 3D printer I used some plastic boxes purchased customized by me. Sparkfun has some https://www.sparkfun.com/search/results?term=enclosure&what=products. I used a local shops with much more possibilities http://www.platan.ru/cgi-bin/qweryv.pl/0w41603.html
3D is the best way but very capital angry
An example of 3D printed box:
I personally prefer to use custom build hardware like maniagbug did http://maniacbug.wordpress.com/2011/10/19/sensor-node/
Pro mini 3.3V will consume less running power because of 8mhz clock but i think will be the same power while sleeping.
Nano is easy to use because it has USB->UART converter on board and LDO 3.3v on board. Etc. you do not need an external components to program it and to connect radio module to it (radio requires voltage bellow 3.6V).