If you like Treks, look around for a closeout '13 Soho Dlx at a local or not so local dealer. You will need to upgrade to a dyno front wheel and drop bars, but rack and fenders come with. Only downside is the rear brake is Shimano roller brake, not disc.

I work at a shop that is a Spot dealer and we built a drop bar Ajax for a customer. Once we got done swapping out parts, it wasn't too much less than $2k.

OP is really asking for a lot--belt drive, disc brakes, dyno hub, drop bar/IGH setup. Once you add in fenders, rack, kickstand?, lighting, etc. I don't think you'd be under US$2k.

Personally, I'd stick with rim brakes, and ditch the belt drive from my requirements. That would get the price a whole lot more reasonable for not many drawbacks.