>Its value, after payment of the Roman Empire’s 25 percent import tax, was nearly seven million sesterces, which scholars have calculated was easily enough to buy a luxury estate in central Italy, or, if you prefer, to pay 40,000 stonecutters for a year. That translates into some vast fortunes.

Aparrently this value from one ship, and it's reported to have 100 ships per monsoon season to Indian Ocean, it means per year since you need to have two monsoon for departing and returning. This report is for the first century AD, before the trade route reached its peak.