Except for a very few brands, watches don't hold their value very well. Think like a car, most lose 50% the moment you step out of the door of the shop. That means you can buy a lot of used watch for $1-2K, I know a lot of folks here bash used watches, but once you put it on, it's used anyway. On the other hand, if you get a watch used at a good price, you can pretty much always get your money back out.
Though I'd be happy to have an IWC Portuguese (the Panda, black with white subs), I've never much wanted a watch that retails much over $4K (OK, I had a thing for a Zenith once, but nothing ever came of it) and I've never paid over $1,800 to get any I own. My Omegas (Aqua Terra & Speedmaster Broad Arrow) Sinns (142 & 956), and IWC GST Chrono are all well constructed, long lived, and I love to have them. I doubt I'll ever sell any of them, though I did sell off my first "nice" watch, a quartz Tag, and gave a Movado Vizio I'd stopped wearing to my wife. I'd echo avoiding quartz altogether.
Jimmy's cut off of $2,500 retail makes sense, though there are some great brands that slip in under that cutoff. If I were going to have only one watch, I'd get a used Omega Speedmaster (around $1,800 used with box, tags, and original receipt from authorized dealer if you look around). With a few straps (black and brown, probably croc) and the bracelet it comes on you can dress it up or down as much as you need.