Does anyone know if EXP scales when you level up? Like, will lower level recipes give you less EXP as your level increases?

What is the difference between the amount of EXP given from lower level items and higher level ones?

Is it cost effective to bake a bunch of lower level goods instead of making some at the current unlocked level?

The EXP depends on baking time, not item level. The longer, the better. At certain levels (like 18-20 and up) baking a thing that takes an hour will give you 1% EXP or less. And items that take like 20 minutes will basically make no difference to your EXP until baked in huge amount.

What is cost effective - baking the recipe that takes the longest but doesn't include currently inflated ingredients. But it gets costly no matter what cause you will have to bake hundreds of things anyway to level up the further you go.

It takes more EXP to advance to higher levels. The amount of EXP given per minute is not known to the players. Because it takes a whole ton of EXP to go up a level, it's quite typical to bake stuff just to bake the stuff over and over again, and not worry if it can be sold for value added. Baking is popular and many recipes share the same absolutely necessary choke ingredients, so it this process will become very expensive the higher you go up Me I'm running away screaming, waiting for the price to go the heck down.

Staff does quietly mess with the true rarity of items (usually the choke items) that get super-inflated by their own standards to reduce the prices of those things. Eventually. An example of the market in choke items goes like this. After the recent Achievements that required your pet to eat Baked goods, the price of Baking Powder went from 70~80KsP to 1.2MsP. Baking Starter Kits, which have a fifty/fifty chance of dropping either Baking Soda or Baking Powder had their frequency upped, a lot, in the Bathhouse.

As recently as two weeks ago the price had dropped to 250KsP but either a second round of speculation or more people deciding that this was an acceptable price to bake with (wtf?) happened and now it is back up to 500KsP. Notice Baking Soda is dropped into the game of Subeta along with Baking Powder at the same rate. For whatever reason, nobody is fucking with the price of Baking Soda as hard, and so it has gone from it's Achievement high of 400KsP to below 56KsP. Baking Soda was a bit cheaper than that usually so this is not an awful price, just a high one.