You can't determine the price of artworks based solely on the quality of the art.
MilesDF can charge those amounts because people are willing to pay for his signature.
Demand sets your prices. If there are people out there willing to pay a certain amount of money for your art, then that's the price of your art.
Most smart beginner commission artist start by giving their art a "fair" price based on how much time they spend on it.
You want to make 20 bucks per hour? Your average artwork takes you 5 hours? Then charge 250 bucks for it (50 to cover taxes, fees and promotion time).
- Are people reacting positively and sending you requests for your services at those prices and you can meet the demand? Great, keep going.
- Are people flooding your inbox with requests and you can't manage the huge demand? Fantastic, increase and keep increasing your prices until the demand is manageable.
- Are people ignoring you even tho you are promoting yourself by posting your stuff on socials all around the web? That's too bad, apparently something is wrong and you'll have to lower your prices to attract a clientele. But with that you'll probably need to increase your delivery speed or drop your quality until you gain more traction.
You can't just ask how much you should charge based on your best artwork. This simply isn't how things work in the commissions community.