If you're on such a low budget to begin with I don't believe a used RC is the place to start. Especially a used nitro RC. While they may be less expensive in the beginning it will more than likely end up being more expensive to replace, upkeep and maintain since most parts are already on their way to the trash bin. I would suggest saving up just a little bit more money and either purchasing new or finding another low price deal like you have, but with a little more of a cash buffer in case something does go wrong down the road.
If the Hobby Shop the Jato seller is referring to is correct this is what is needed for replacement:
http://www.amainhobbies.com/product_...--4x14mm-BCS-4
However, the Jato seller didn't sound like he was very educated about his product since he both wasn't sure about the name of the replacement part nor did he have the drive to fix it with what could be a simple $12 part. Since he doesn't seem very educated, there may be more than just that $12 part broken.. Plus, no pictures, no nothing...? Meh..
Cheers,
Kyle.