Can I keep repeating spells until I have no runes?

No, you cannot.

According to Rule 820.1.c.3 and RiftJudge FAQ #9252, each individual instance of the Repeat keyword on a spell can be paid for only a single time.

Even if you have many runes available, you cannot pay for the same instance of Repeat more than once. You must decide whether to pay for the available Repeat cost(s) at the moment you play the spell from your hand. You cannot add additional repetitions retroactively or continue to pay for them as the spell resolves.

If a spell has multiple distinct instances of the Repeat keyword (for example, one printed on the card and one granted by another effect), you may pay for each instance separately, but each instance still only allows for one additional execution of the spell's effects.