Raising prices, or changing the effective price according to the size of the pre-purchase, is a reasonably common approach. It's justifiable in most cases, and it works, if you're careful.
So the real issue - the question behind the question - is how to get a price increase through, without alienating existing customers.
You need to start off by doing some analysis, looking at buying behavior in your established base. You need to identify the main patterns of purchase and usage - for instance, do bigger purchasers tend to buy more frequently, or buy larger blocks? In the data there will be some big clues to segmentation. So make a tentative breakdown into two, three, maybe four segments where you find similar behavioral characteristics.
Now look at how the price change you're thinking about would affect each segment, (a) if they continued their present spend/use patterns; (b) if they optimized their expenditure by buying larger/smaller blocks; (c) if they locked their spend at present levels by varying their usage. Work through the winners and losers per segment, and think about how you would communicate the changes in each case.
Then experiment with different ways of making a price increase, and repeat the analysis. For instance, alternative ways to increase your price and introduce the relation between credit block size and discount include:
Raising the price of a single credit + introducing a new 'super-size' block that matches or beats the 30 cents
Leaving the 30 cents intact, but raise the first tier, i.e. if you could previously buy 10, 50, 250 credits, the new minimum might be 50, or 25, or some other figure higher than 10
All of this will help you get underneath the question of what the price increase will mean for your consumers in each segment. This arms you both to choose the best way of creating a targeted price increase, and to communicate meaningfully with existing customers around that increase, possibly using special offers to soften the blow (and bring forward revenues).
All of that takes work. Trust me, it's worth it!
Finally, it's worth bearing in mind a pattern used in consumer goods to make price increases. Let's invent Grungies: just one Grungie added to your wash makes your delicate clothes last longer. They're sold as a pack of 50 for a typical retail price of $5.
So that's equivalent to 10¢ per Grungie, right? Yes at the moment, but that's going to change.
So you want to push through a price increase equivalent to raising the pack price to $6 - a 20% increase. But you don't want to lose out.
Your first step is to introduce a new convenience pack - 10 Grungies for $1.50. You run that alongside the current pack and pricing. Sales figures help you validate whether a market for Grungies at significantly over the current effective unit price.
You now have four cases.
First, it may be that the indications are that you can not only increase the price, but that you may be able to increase by more than the 20% target. Woot! You now have all kinds of options.
Second, it looks as though there's room for a price increase, but not at the 20% level. Your next price move is going to be to try and zero in on the level the market will bear - again, there are several options.
Third, it looks as though increasing the price will have a negative effect. In that case, the next theory to test is that a price reduction may actually increase profit. Look at that! We're off on another track, without ever upsetting existing customers, or having to go into reverse.
Finally, it looks as though the 20% is realistic. Raise the price of the 50 pack to $6, and soften it with a temporary promotion - 64 for the price of 50, say. That promotion was slightly better value than the old offer, and when it ends, the new pricing's in place. All that's left to do is to tidy up - work out whether having two pack sizes instead of one is an improvement, and if not, what the optimal size and price will be.
Now, go round your local supermarket and start taking guesses who's in the middle of testing price increases! (Bear in mind that in the real world of consumer goods, there's also competitive pressure, so approaches that signal intent without opening too much of an opportunity for competitors to jump in opportunistically and steal market share.)
By thinking through these simple but high stakes sequences, you'll understand better how you can achieve similar results yourself, and what promotional tools you can use to maximize your results and minimize your risks.