ive had my fans tell me that 50% off for another character isnt good, you wanna have a price for characters across the board
i recommend breaking it down like this
1. consolation (sketch, poses, data gathering, "these are my ideas for the piece") if they green light you (they like everything) ask for the full price right there. The sketch is ENOUGH to prove you're doing it, and if they dont want to pay now they wont want to pay later. (ive been doing this for 20 years [im old], dont fall into that trap)
2. invite them to a stream or tell them how the picture is going from here on out. (they did their end, now you gotta hold up your end!)
---
2-0 your base fee should be however much money it would take for somebody to rip you out of bed and NOT be too mad. For me im pretty chill, so 5$ for me would get me to be confused but not mad. ALWAYS, ALWAYS, ALWAYS ask for this. Some people call it a tip, I call it my "grumpy tax". You add it on so you can haggle, and so if there is tax collected on your art you wont notice that much. If none of that happens you've made sure you got your tip, and a tip makes you feel good. Some people need a little more "grumpy tax" than others. Professionals call this a consultation fee

And if youre too shy to ask for a tip upfront this helps you get that confidence.
(price setting)
2-1 refine art lines and correct: even if this step takes you 45 minutes you charge for an hour of your life. Minimum wage is 8$ here. I used to sell my art for 2$ a hour (often times turning out to be more like .30) and it did NOT feel good, and it attracted customers who didnt care if i felt good.
If youre going to attract a customer you have to trust me here: when the art fairy comes by to drop you off a customer IT IS NOT ABOUT YOUR PRICE if youre low they might want more from you... but generally speaking people have X amount to spend and dont want to task you with more than one comm. So they will task you for 10$ and task another artist for 10$ ... you want the whole pie, not a slice! You help your fellow artist not by making sure they have a slice of your pie, but by making sure that there are more pies to go around for everybody and that there are no fights over any one single pie (commission period).
TIME your art stages, how much time do you spend drawing?
MONEY don't go below minimum wage, charge however much someone would have to pay you per hour to sit around and watch somebodys annoying kids.
(not that you dont enjoy your work >w<' but if you want to do what you love for a living you gotta make enough to beat something else you could do that would make you miserable. art is a COMMODITY, not a necessity. Its a luxury item. You are a theme park owner and your rides are art! People WANT to go on the ride, and you should NEVER feel like you have to let them on for a penny less than what its worth. NEVER haggle a penny less than your consultation fee. )
2-2 do the art thing you do, but check in at each stage because people like that. If they ask you to change something on a whim (something that was NOT stated in the sketch phase) charge them for it. How much? How much time did it take for them to convey that? How much time will it take to do it? If its small and easy, charge the amount of a cup of coffee. If its going to take you a significant amount of time you can charge your hours or charge the amount it will take for you to go get a lunch break.
When you're done give'it to em

------------
TLDR:
Tip/ Consolation fee : $10? $5? $20? How grumpy you feelin?
(How much money does it take for somebody to barge into your personal space and get away with it? Charge how much you would want if you had to spend an hour dealing with angry, and mean people? [commissioners are generally nice but there are some rough ones out there!])
How many hours will this take? 3:00? 5:30?
How much would you get for watching someones brats? $10? $15? $20? $25?
(Hours) X (Money) = Base Fee
Did they give you any trouble? Did they ask you to fix stuff that they never specified? (Yes?)
Charge em for:
A.) A nice relaxing cup of wholesome (You're gonna need it after that! >w<)
B.) Lunch for one! (Working hard makes me hangry!)
C.) Every hour spent actively wasting your time (don't wait around all day for them to respond to you, have 2 projects open at any given time.)
D.) Twice as much for every hour that they spent being rude to you. (Make an example of them! Nobody will push you around!)
Hope this helped

If it did you should totally come check out my page!
Userpage of BedsheetWalking -- Fur Affinity [dot] net