If you reload, you can get dies (Lee), 100 pieces each brass, and bullets from Midway, for about $75, about $25 more than a box of loaded ammo.
At the time I was looking, about a year or so ago, I looked pretty much everywhere online, and was only able to find two boxes of loaded ammo (smokeless), and they were both about $45 a box plus shipping.
I found an S&W 4th model top break in my dads drawer when he died. It was in real good shape, and locked and timed up well. Didnt know the caliber, as they arent marked, so it took a little detective work. Being an S&W made it a little easier. I also found out it was a black powder era gun, and most of the recommendations pushed me in that direction.
Ive had a couple of other similar guns over the years, H&A's, and Iver Johnsons, etc, that while decent looking, I would not have shot them, as they were pretty sloppy in lockup and timing. You may want to consider looking closely at that before you lay out the money for ammo or components. The S&W I have, other than some surface patina, looks/feels like it had little use.
While doing the research, I got a lot of conflicting info on the use of smokeless loads in the BP era guns. Many said it was OK, while others said it was a bad idea, and would likely stretch the frame. I chose to err on the side of caution, and went with BP.
This is my S&W with some of the reloads......