1 denarii in the late republic epoch was fairly 70-80 dollars today, i think 70 million dollars(in roman tiems) is enough to buy your way to whatever you want. Macrus Licinius Crasus was the most wealthy roman ever (it is said) and he made his wealth through real state, fire and raping(some things never change)... So he would buy off auctions houses from dead people or politicians in exile, and also creating a fire brigade that charged you money for not letting your house burnt down.

But if you were to be a merchant, that in roman times it was huge, probably the most lucrative one was importing spices from India and selling olive oil and gold to them, also some textiles. Although this wasn't part of your question, I will warn you that if you are planning to go back to the 0AD (cool, take pics) and taking a "small loan" that wouldn't be enough to start your enterprise, since trade in that time required, lots of contacts, knowledge of the cultures, of the courtmanship, of different languages, trade routes, and mostly good position in the roman aristrocracy. If by any coincidence your last name is Iulius, Brutii, Flavius, or Aemilius, then sorry, but if not i would advice you not to try it.