Where does Eggman get his funds from?

[charmsb]

he gets them from deez nuts

[CertifiedNobody]

Eggman has his robots mining off-planet to continually produce materials for his machines

[SBR2]

Zero Gravity shows that he owns companies. I'd assume he purchases stock under an assumed name and creates consumer robotics while using all the funds for world domination. 

[Dr. Mechano]

7 hours ago, charmsb said:

he gets them from deez nuts

Strictly speaking, this is a plausible explanation. It'd just take a very long time.

In the Chao Garden, the orange fruits - referred to by Omochao in the tutorial as nuts - can be brought to the Black Market and sold for 10 Rings. Now, Eggman can only carry one nut at a time back and forth between the garden and the market, but this is a reliable (if inefficient) way of expanding Eggman's capital.

Get to work on those trees, Doc!