Nobody commercially makes dummy SINCGARS. You basically have to watch eBay and the classifieds for a very long time if you want any kind of deal. Occasionally people list complete two-set early SINCGARS setups for something just shy of $10K, but those people are hitting on the recreational chemicals a little too enthusiastically. There were some training model SINCGARS sets that could be modified to fit the VAA trays, but they also show up rarely.
If you went with the older generation VRC-12 family stuff you could do a complete setup fairly reasonably (HMMWVs were in use from '85 up, and the older installations were around through the late 90s) - as there's lots of that stuff out there. Other than that, read the manuals, get a handle on what you need, and just keep scouring eBay and the Classifieds here and on G503 and grab it as it shows up.