42nd street camera has been around for a long time. They used to be well known as a bait and switch outfit with many people reporting problems like receiving open box stuff and the store refusing returns. Perhaps they have cleaned up their act, but personally I would avoid them like the plague. Here's how the bait and switch works. You place your order for something that's way cheaper than everyone else. A day or two later the store calls you and says they are out of stock. Then they try to sell you something else. Another tactic is they say they have the body, but are out of the lens so they try to upsell you on a different lens which is usually non-OEM. When you tell them you want to cancel your order they harass you to no end with rude and aggressive sales tactics.
B&H, Adorama, and Cameta are the ones I've dealt with over the years. All have excellent reputations and excellent customer service. I've never had a single problem with any of those and I've bought a lot of stuff from all three.
Cameta has the Nikon refurbished 5200 (body only) for $529. Every Nikon refurb I've ever bought was indistinguishable from brand new and Cameta gives you a 1 year warranty. They come in a Nikon shrink wrapped box with all the manuals and accessories just like brand new. If it didn't say refurb on the box you'd never know other than the shutter count. As I'm sure you know you don't need a lens for astrophotography with a telescope, but if you want the 18-55 they have the body and lens for $599. If you wanted to save a few bucks over B&H's new price that would be the way I'd do it. The last two Nikon bodies I've bought have been refurbs from Cameta and they are still going strong with no issues.