Welcome to a great sport. I'll start, then step back and let those that know more continue.
I'm a Colt Nut but a great black powder revolver to start with would be a Remington New Model Army, .44 caliber, simply because it has a full frame and you won't have to deal with wedges and loose barrels. Pietta and Uberti make them. Check out Midway.com, or Cabelas, or half a dozen other sites (I like Midway). Or check out a local gun store (where do you live?)
You could save some moola by buying a used revolver, but with a new one you'd have a warranty, usually a year through Taylors and Traditions (they import the revolvers). Price: $180 - $250 (ballpark).
You could buy a brass framed revolver for less money, but they aren't as durable as steel framed (unless you keep the powder charges lower). This is a controversial issue.
Can of black powder - approx $14.00. Pryodex is more, 777 is alot more. I like Black Powder.
Caps (probably #11 CCI or Remington) approx. $3.50 per 100.
Round balls (.454) approx $7.00 per 100
Lubes (Bore Butter for example) maybe $5 - $6 a tube.
Then there's cleaning supplies, eye & ear protection, etc.
Legal issues? I live in Massachusetts where you need a permit for staple guns, but I can buy and receive these revolvers without a license, but I need a permit to own them. Makes sense? No. Basically, the Federal laws don't consider a firearm made before, or based on a firearm made before, 1898 as a firearm. It's alot more involved than that, and local laws apply that may differ...good luck on that one.
Wow, there's alot to this sport, ain't thar? I've only scratched at it. But the great thing is, black powder shooters are very helpful. Watch...