It is an interesting proposal from a marketing standpoint. Leave the sleeves at their current prices.
Single balls could be offered at sleeve price + 20% / 3
Dozens could be offered at sleeve price x 4 minus 5 or 10%
Unfortunately I see this as hurting the income from ball sales. So many of the players who play a lot of games also have the credits built up to buy the bulk of their balls in dozens. I can't imagine there would be enough single ball sales to offset the 5 or 10% reduction in income from those dozens sales.
A better option would probably be to go ahead with the single balls at a premium and hold the rest of the prices where they are. Then, once a month have a weekend sale on dozens, rotating brands each month.