[Ux] How to display quotas to my user without using currency?
Personally I think you could use percentages just fine, you can still apply that to instance rates. For example, 0.02% per hour.
However, if you don't like the idea of percentages I would suggest you display everything as "units" instead. You don't even need to convert the numbers, just remove the currency symbol and add "units" at the end. Something like this:
If you don't like the idea of using fractions of a unit, then just eliminate the decimals by multiplying all the values by 100. Like this:
Just delete the dollar sign. The units aren't important here, just the amounts.
My answer is so basic that I'm worried that I'm missing something obvious, but here goes:
How do you know when a user has exceeded or is approaching their quota? What is actually being measured to tell you that? Bytes (as in storage)? Minutes (as in cell phone usage)? Bytes per hour?
Just use the units of whatever is actually being measured. (If the users aren't paying, I'm not sure I understand why is it being converted into dollars to begin with.)
If you offer multiple services that use different units and the units are converted to dollars as a way of normalizing them into a single value, then one solution might be to change the column headings from "Quota" to "Monthly Credit" (or "Weekly credit" or "annual credit" or whatever time the quota is based on) and the 2nd column to "Credit remaining" (or possibly "Credit used" if you can't change the logic that calculates the value of the 2nd column). The idea here is that use of the word "credit" (or possibly "allowance") addresses the concerns from the users that feel the current display gives the impression that they are being charged.
If you don't think that changing the column headings alone will solve the problem, then another approach would be to just ditch the dollar sign and use units of "credits." That addresses the concern two ways: it gets rid of the dollar sign that some users don't understand, the unit "credits" emphasizes the free nature of the service.