So I had to actually double check this.

Attila did not demand 3000 lbs of pepper when he threatened to sack Rome, that seems to be a modern misconception. I'm not sure how that has occurred but little is known of what demands Attila made of the western part of the administration of the Roman empire. Priscus records the Huns had quantities of Indian Pepper, and that it was also a gift the Romans used in their envoys to the Huns, but says nothing of the specifics of demanding it in any treaties.

Instead that demand comes from Alaric, not Attila. The primary source on the demands made by Alaric is Zozimus' Nova Historiae ("New History"), who states that during the first siege of Rome (there were three sieges from 408-410, the third of which resulted in the city's sacking) that 5000 pounds of gold, 30,000 pounds of silver, 4000 Silk Tunics, 3000 hides dyed red, and 3000 pounds of pepper were paid to Alaric to lift the siege. These are all valuable commodities (notably two of which - red leather and silk tunics - are associated with Roman bureaucracy and military officers).

The value of pepper I will leave to someone else to answer in-depth because Roman trade and foodstuffs isn't my specialty, but the Romans imported pepper en-masse from India through the red sea trade and it was widely used throughout their empire. It was a luxury spice and commodity, and notably was also different from the pepper we typically use today.