After completion of the vampire mission you can go get your reward and it will total 2800 coin.
But if you leave and then come back and accept the reward from the Count of Skingrad again, it will be 5000 coin. You can get it as many times as you want for unlimited money.

Note:

First you have to loot everything, but leave the gold. Then you exit and loot his body again and keep taking the gold (16 gold peices).