A custom frame is going to run you more than $800. I would say you will be looking at 1500-2000 for a reasonable priced frame. That figure is going off of what my buddy just paid to have a custom fram made for a Harley. Metric would probably be slightly higher because most shops aren't going to have jigs set up for metric bikes.
If you are serious about this you should consider getting in contact with Coyote Customs out of Oklahoma City. They are very hard to get in contact with. The builder is almost like a frigging gypsy. He specializes in metric bikes and builds custom frames for them. I have also heard he is very reasonable on price. I have seen some of his bikes in person and the work is top notch.
The warrior will not be a good bike to start with anyway. Way to many parts with the fuel injection and electronics. If you are serious about a metric bobber I would suggest starting with an older carbed Roadstar. Way fewer electronics to work around.
You are going to have to be realistic about price though, I promise you $800 won't even get you started.Not trying to be a buzz kill man, just trying to let you you know the facts.
Good luck with your project.
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"Those who would give up essential liberty to purchase a little temporary safety deserve neither liberty nor safety."
Benjamin Franklin, Historical Review of Pennsylvania, 1759