Not an item suggestion, but still an item shop suggestion:
1. Decide a clear percentage for weekend promos (like 40 or 50% on every item). That will make some items more expansive then now and others cheaper than now, but it makes clear what you save in offers. You don't even need to decide a fixed percentage for every promotion, but for one promotion, each item should have the same percentage. You could even use this to advertise the promotion as X% promotion.
2. Adjust the ruby bonus for normal prices so every item gives nearly the same number rubys for each diamond. For example at the moment if you buy 10 charges for the transmutor you get 1 ruby for 3 diamonds, but if you buy 100 charges you have to pay 6 diamonds for 1 ruby. Since we need a lot of rubys due to the high prices für perfect plussing stones, we should get the same rubys per diamond regardless of what we buy.
This would also allow, for example, special promotions like "no less diamonds, but 100% more rubys" without getting laughed at, because other items out of promo give way more rubys.