Silksong is famously stingy when it comes to its chief currency, especially in the first third of the game. After about five hours you'll probably find that you don't have enough money to unlock fast travel points and benches, let alone buy all of Shakra's maps, let alone buy that Simple Key back at Bone Bottom. I found myself in that situation by the time I hit Greymoor, but after a while I realised there's a brilliantly lucrative farming spot just nearby that you can exploit endlessly.
Not only that but I'm pretty sure this was designed to be a farming spot, because there's a bench within 10 seconds of a mob of zealots who drop around 29 rosaries per run. That means you're looking at around 60 rosaries per minute, or around 300 per five minutes.
You'll need to head to the Halfway Home (see the map above), which is conveniently close to the Greymoor Bellway station. Just hop up there, rest on the bench inside the Halfway Home, and then move two screens right. You'll see these guys:
Whack them. Have no mercy. Then run back to the bench, rest, and they'll respawn. Go whack 'em again. Rinse repeat. [[link]] Every couple of runs your silk spear will replenish too, which will make whacking them much faster.
If you've saved Bellhart, you can quickly catch the Bellway there and invest your Rosaries into beads. If you've got the time and patience, you can become very rich. I'd recommend putting on a nice movie while you [[link]] do so. Perhaps this [[link]] nine-hour documentary about the decline of a Chinese industrial district.
If you're up to Act 2 already, Sean has a good place to rack up Rosaries at around 3,500 an hour.