Here's why:
* "Here, borrow my money..." This is grammatically correct but implies a more casual, immediate offer.
* "I will lend you money..." This is also grammatically correct, but it's a separate statement.
* "Either...or..." This construction is used to present two options, and in this case, it clarifies that the speaker is willing to either let the other person borrow their money or lend it to them.
Therefore, "Either borrow my money or I will lend you money" is the most grammatically correct and clear way to express the intended meaning.