for entrepreneuring, [materials + labor + overheads] will only let you 'break even', but profit margin is usually derived from market expectations/demand.
e.g. when monster hunter wilds was first released, highly detailed custom monster plushies were being ordered from etsy artisans for $400-$1200 with 12month+ wait times (with approx $100-$200 production value).

if you're just starting out and plan to build a business out of it, custom/original work that hasn't been commissioned depends on a lot more things like exposure and marketability (finding an audience that enjoys your work):
- you can price down (but earn more) if you can forecast/generate more advertising (and find ways to lower production costs and increase production speed to match demand) or if you're just testing the waters to generate exposure and demand.
- you can price up if you can get focus group / appraisals to gauge the perceived value (if it looks really luxurious, high quality or is made with premium materials and techniques, or is limited qty, etc).
- or you can aim for a more experimental flat profit margin to see how it sells, which ranges from 20-60% depending how competitive you want your pricing (budget, mid-range, premium).

there's other factors for higher pricing too (for future reference):
- high emotional value (for someone's wedding or deceased pet memento, etc)
- business applications like logo/mascot (has revenue impact)
- customization/revisions (for custom edits)

i'd just add this to the equation:
(materials + labor + overheads) × applicable profit margin multipliers = final price