I use this, all the smart stuff is from the internet.
A can of 5l isopropyl is about 25 euros and I mix it into a normal cleaning spray thing thingymajig.
-smart stuff-
There are 3 main parts to a degreaser:
Alkaline booster, to increase the pH, allowing the dirt, grease and grime to be effectively removed, for faster cleaning
Solvent, to cut through tough grime and grease, as well as extract grime and grease from hard-to-get areas
Surfactant, to hold grime and grease in the cleaning solution, preventing it from depositing back on the bikes surface once lifted off by the solvent and the alkaline solution.
50% isopropyl
40% Water (H20)
5% Sodium Bicarbonate (Baking Soda)
5% Dish-washing Liquid