Re: JEM Custom Build...sources/recommendations?
Well, for a cost-efficient project you should check out Nate Perle's site. He sells raw Jem bodies for 99$. You would have to paint it yourself. If you have a donor guitar like a 550/560/570 or any aanj neck guitar you can use the neck from it. Aiguitars on e*ay sells pre-routed fretboards you could put on the neck. Hardware is best purchased from Rich Harris from IbanezRules(banner above). If you want a higher quality guitar, or you don't have the confidence in building it on your own, you schould check out ETGuitars (baner above). For example, i asked him for a quote for LNG body and neck. It was around 900$. Also Check out his Marble guitar series.
AlaskaBat has a DIY guitar building blog running, it is well worth reading.
I hope that helps with your decisions.