Hi. I'm not sure if this has been suggested before. If it has then I apologise for repeating the suggestion.
With unstable prices of plushies and flowers recently. It's hard to to know what you paid for them on average. And therefore, those of us who build sets or try to resell at higher price, it's not easy to know what our average buy was at per certain item.
Obviously if you buy 100 crocus at a set price then you know how much it's cost and can sell on easily or exchange for points in your set's with an overall figure of what those sets have cost.
If, however, you build sets to about 200-300 then your buy price per certain item is gonna fluctuate so much that it's hard to even know if you're selling your sets on at a good price or not.
With this in mind i suggest the devs put in an "average counter" which adjusts every time you add to that specific item. This way we will know what we have paid overall on each particular plushie/flower and can make better decisions on what price to resell on.