I ask everyone the same question: Do you feel confident on a bicycle? If the answer is no, then maybe you should reconsider. If the answer is yes.....
I would skip the Royal Enfield. I own one. I like mine, but its a toy. Fun for hauling around the neighborhood, or up to a coffee shop, but not really adequate for American Roads. Triumph would be a much better bet. You can get a solid Bonneville for $5-6, a bit more if you want a newer EFI model.
If you have zero seat time, get a mechanically sound but cheap Japanese 500-600. Enough power to feel confident on the road, but if you dump the thing, you won't feel bad.
2005 Kawasaki Ninja 500