You can farm for Blood Echoes (and Blood Vials) quite early in Bloodborne. But first you need to defeat the Blood-Starved Beast in a ruined church at the bottom of Old Yharnam.
This will cause the Snatchers to appear around Cathedral Ward. So go there and get killed by a Snatcher.
You will now wake up in a prison. Leave the cage and ascend the stairs, and reach the lamp of Hypogean Gaol (which in fact is in Yahar’gul, Unseen Village).
Fight your way through the main hall and exit the building.
- Outside Hypogean Gaol. Wait next to the stairs for the Giant Pig to reach the top where the note “Behold! A Paleblood sky!” can be found. Kill the bloody pig.
- Advance forward on the main street (left of Hypogean Gaol).
- On your left side there’s another Giant Pig. Dodge the attack and then kill it.
- Continue up the streets and kill the Rabid Dogs. Pick one at a time.
- By the end of the street there’s a Snatcher and two more Rabid Dogs. Ignore them, and turn back to the Hypogean Gaol.
Follow the alley to the left of the building and open a door to the lamp.
Return to the Hunter’s Dream.
Now wake up at Hypogean Gaol again. Take the shortcut that you’ve just opened so that you don’t need to fight the relatively tough Snatchers in the main hall. Repeat step 1-5 above.
At this point of the game, every time you wake up at Hypogean Gaol – before you kill Rom, the Vacuous Spider – the Giant Pigs and the Rabid Dogs will respawn, and these creatures are pretty easy to kill and will get you over 10,000 Blood Echoes each iteration. The Giant Pigs are also likely to drop Blood Vials.