How to handle unsupportive family members?

Have you thought about giving it a shot? The face up I mean You can always wipe it away and send the doll out to be painted if you can't do it yourself the way you want it done, but the thing is - you will never know if you can if you don't try. Seal the doll properly and the face up can be removed easily enough.
Sometimes being pushed out of your comport zone is what makes you realize that you have abilities you never knew you did. And sometimes a parent does exactly that, whiter they realize it or not.
I don't know your mom, so giving advice is really not a good idea, but if you, even for a moment, think that she is cumming from a good place, place of caring and believing in your talents, than give her a chance - she may be right, and if she is not than she will be much more open to you sending the doll out for commission after she witnessed your lack of painting skills first hand and resigned herself to the fact that her darling wants to make outfits not faces

 

Owning a piece of art by someone you admire is great, but so is adding your own artistry to a piece or art that is already there - the doll itself To me it is almost a way to claim ownership of the doll for real... The face up done by someone else is althou something you have to be careful with - it would be a shame to damage it in any way and removing it if you want a fresh one? I doubt I'd ever do that...
Your own work thou is something you can mess around with and than in a year or two decided to abandon with little to no guilt - you had fun, you learned stuff and now it's time for something else. So giving it a shot and changing your mind works, the other way around? Not really

 

If I were you, I wouldn't have told my mom the true price. In my experience, people who don't collect pricey works of arts, wouldn't get it. For example, I told my dad the actual cost and he's fine with it because he collects model steam locomotives and their accessories which can be quite expensive. My mom, who collects nothing of value and buys stuff on sale simply because it's cheap, would never in a million years understand it. So I lie about the prices to her. I would be in the same boat as you if she knew how much I spent on this hobby. You don't have to feel bad for enjoying BJDs; yes they're pricey, but life is short, treat yourself because you deserve it. Spend your money on what makes you happy and not on what your mother would consider appropriate. If she doesn't approve of your spending habits, that's her problem. It's not like you are wasting your life's savings or selling a kidney for a doll.

And for the face-up, if you are worried about painting on a 3D object, you can always practice that skill on thrifted dolls like Monster High or Bratz. But if you really like that artist's face up, the $70 is worth it. If you think about it, $70 is about the price of a new haircut and color at the hair salon or 3 trips to a restaurant, something like that. The $70 face-up will be permanent unless you decide to change it.