When a spell says repeat, can I do so multiple times as long as I pay the cost?

No, you cannot pay the same instance of the Repeat keyword multiple times.

According to Rule 746.1.c.3: "Each Repeat Cost can be paid only a single time."

While you can only pay each individual instance of Repeat once, there are two ways to execute a spell's effects more than twice:

1. Multiple Instances: If a spell has more than one instance of the Repeat keyword (for example, if it has the keyword printed on it and is also granted an additional instance by another card effect), you may pay for each instance separately. According to Rule 746.3, the spell's instructions will be executed an additional time for each instance of Repeat that is paid for.
2. Granting Repeat: As noted in Rule 746.1.c.2 and Rule 2163 (from the RiftJudge FAQ), if a spell has multiple instances of Repeat (one printed, one granted), you can pay for each separately.

In all cases, you must decide whether to pay for any available Repeat costs at the time you play the spell from your hand. You cannot add Repeat retroactively once the spell is on the chain.