What is the proper plural of "reputation"?

Reputation in this instance is being used as a mass noun, and mass nouns do not normally take a plural. It is somewhat unusual in this case that there is no count noun to serve as the measure word, i.e. we don't say "125 points of reputation" by analogy with "125 grains of rice". Nonetheless, the formulation given above is what is normal and idiomatic for this scenario.

There are other words which exhibit this same pattern:

• Getting to level two requires 5000 experience.
• The Vorpal Sword costs 300 gold.

All of the examples that come to mind here are related to technology or gaming. I don't know if this is an actual trend, or just selection bias based on what's in my brain.

Reputation is not the unit, its the object being quantified. Technically, it would be

Vote Down requires 125 points of reputation

But this is awkward and we all understand that reputation is an arbitrary number with no real unit. Saying "How much reputations do you have" would be akin to saying "how much strengths do you have" or "how much sauces do you have?"