In order to build this module, you will of course need to first locate a genuine Spektrum, Horizon Hobby (or other OEM DSM Transmitter.   It seems as if the following models are currently the cheapest to find for DSM RF Modules.

1)  DX5e  - Spektrum 5 channel radio (Ebay for approx $45 or so?)
2)  MLP4DSM  - Horizon Hobby (Blade) 4 channel radio  (Ebay for approx $40 or so?)
3)  DX6e - Spektrum 6 channel radio - (Ebay for at least $150 + )  -- by far the most expensive route

I'm sure there are others as well that use OEM DSM RF modules, these are just the first 3 I know of..

It's quite easy to unsolder the RF module from the OEM tx board, with a good large-tip iron for plenty of heat, and a nice spool of copper solder braid.  With these two tools, you can easily heat up and suck up the solder around the pins, and then pop out the RF module.  It's normally just held on the top side with some simple double-sided foam gap filling tape.

DX5e Module - TOP

DX5e Module (Bottom)  -  Part Number:  X1TX0 REVB

MLP4DSM Module