i say that it would be fun to make a recipe that when it is made, it will increase your alchemy skills by a large amount. mainly because you don't sell all the stuff for making certain items, like bottled moonlight, or other such things that for some reason you can only find in the market place. i think it would be fair to let people make stuff with alchemy without having to spend a fortune on other items that are needed to make the item, when the total spent on the components is more than the item costs in the marketplace. please take this into consideration.
Also maybe change the RIG recipe requirements. Considering that they require hard to obtain items, where expense REALLY adds up, for something you pay Gcash for, you're only going to cause item extinction. (elegant mint ruffles for double rainbow is a great example no listings on the market at all.)
not sure if this was mentioned yet, but how about being able to craft some of the rare bugs from towns, like the great monarch butterfly? Tough and expensive to craft, but still obtainable.
I love this idea, because I've encountered that butterfly a total of once in my time here, way back years ago. And that little bug has inflated like no one's business.
Besides, we can already upgrade our fish to something higher up the scale. Should be fairly easy to tweak the bugs the same way. Preferably as a level two or level three formula, given that the formula the butterfly is an ingredient in is itself a level three item.