Food
5 star: ~1200 crowns
Amount needed? ~4-6 per level average?
~400 * 1200 = 480000
Favorite food
1 star: Level 1 - 14
2 star: Level 15 - 29
3 star: Level 30 - 49
4 star: Level 50 - 69
5 star: Level 70 - 89
1 star: ~500 crowns
2 star: ~900 crowns
3 star: ~1100 crowns
4 star: ~2000 crowns
15 x 500
15 x 900
20 x 1100
20 x 2000
= 7500 + 13500 + 22000 + 40000
= 83000 crowns
Additional costs
Sprite pod: 2100 energy
Evo Catalyst: 125 energy
Advanced Evo Catalyst: 250 energy
Ultimate Evo Catalyst: 525 energy
Total: 3000 energy x ~75,50 crowns/energy = 226500 crowns
Total
food: 480,000
favorite food: 83,000
additional costs: 226,500
Total cost first pet: 563,000
cost for supply depot pets: 789,500
The biggest cost seems to be the material, but I need better estimates.
After about level 40, I started recording exactly how much food my sprite required. I've posted a fragment of my data in the "Heating" section of the wiki article "Battle Sprite". Do you want more data like that? Let me know.
If you're doing this just for yourself, then do it anyway you want, of course. But if you're doing it for the community, then I recommend that you not convert everything to crowns. Experienced knights have a lot of materials sitting around, that they can't be bothered to sell.