I use paper towel for hatchlings/babies and then pine shavings.

I've tried many different substrates over the last two decades and honestly, pine shavings aren't pretty but it's the most cost efficient when you have a large number of cages. Cost is around $8-10 per compressed large bale that expands to 297 liters! To give you a rough idea of surface area comparison, the large carefresh bales sold in petstores are only 60 liters for around $20.