I was always suspicious of anyone selling a vehicle that "only needed a battery" or "only needs a starter". It seems to me that if everything else was OK, it would behoove the seller to put that part into the vehicle and be able to sell a running vehicle, probably for more $$ than non-running. Tell him to buy the battery and install it, and you will pay for the battery and a little extra if everything works OK. Stress that you will be under no obligation to purchase the bike. If it doesn't start and run, you can walk away without taking any risk.
That said, there are lots of good deals on Craigslist, because many Rebels are used as a beginner bike, and many are sold when the rider gets more experience and wants more motorcycle. $2000 should buy a bike with less than 5000 miles, and at least 2008 or newer.
Troll Craigslist for a few months and write down prices, year, miles and general condition. When a real deal appears, you will recognize it immediately, and can move on it confidently.
When all's said and done, there's more SAID than done.