Some value the ones made before John's death a little higher. With that being said, we'd have to know which model it is. If you knew the name of the model, it would make it much easier to research. However, if you look on the true gun value site, there was a 16" gen 1 that sold recently for $1,200.00..
IMHO - $1200 is about right for a vanilla Gen 1 - that was factory built - yeah, some models will bring a bit more, any details would help.
About $900 for a home brewed rifle - the barrel and receiver set are the main attraction to a knowledgeable buyer if it's been assembled.