@MexicoMike Above is the short version of my opinion. If you really want to buy online, I would consider Champlin the only online service available, watch their site for what you want, buy from them, then go there to check it out firsthand and be fitted for the gun of your choice. At least talk to them about your fitment and other needs if you absolutely cannot go there. Honorable mention: talk to JJ ahead of time your intentions and if he can help you after you've purchased elsewhere; I'm not sure any/all doubles can be rescued or if he will work on just anything (?)
On a whim, I decided I wanted a double and started researching extensively (as is my custom). I already had Mark Sullivan's books from a long time ago (for inspiration) and recently bought Graeme Wright's 4th edition (for knowledge, because I handload). After spending time on this forum I realized, in short:
Don't buy any double on the internet sight unseen, especially if you are a novice (like me). I buy online all the time all manner of firearm without issue and I had my sights on a couple, ready to pull the trigger, but the double is a special beast requiring a different strategy, especially if you are going used/vintage.
I really want vintage, maybe even BPE (I load that also), and I'm afraid to go that route alone, so I'm planning to get help from an expert. To tide me over whilst I study and shop, I bought myself a second-hand A-bolt project gun in 375H&H and a NIB Safari Express in 416Rem (both online) for a tenth of what a serviceable double would cost. Your stated budget sounds like me: you can PAY for a double but maybe can't afford it, probably don't NEED it, and you're willing to stretch to make it happen anyway. This, I believe is how one can buy the wrong thing and be disappointed. Or maybe one gets lucky?
The beauty of a bolt/lever/single is any of these can be loaded down to pipsqueak level or max loaded for magnum performance and sighted in on the fly for any load. A double is different; it's intended for (essentially) one load at one distance for one thing, so it has to be right out of the gate. This may be achieved easier in a new double, but the load situation remains. If you go new, why not buy a Chapuis from Champlin where they are willing to act like a manufacturer rep? Well within your budget and they will make sure it's right for you.
I'll be following to see how it turns out for you. Good luck!