Speaking only for myself, it would be impossible to quote any monetary figure for something like this without knowing more information. For example: do you need the geometry for 3d printing or is it for a game/VFX asset (these would usually have different pricing structures based on time and work involved). Do you need the entire character or just certain armor elements from the sketch? Is the model going to be a one-off exclusive product for a studio project or will we retain the right to resell the asset in marketplaces, like here on CGtrader?
I'm sure there are some modeling hobbyists or enthusiasts out there who would be happy to work on it just for fun or as a learning experience, and there's probably someone that would be happy to do it for between $0 to $100 no matter what it's for. However, I think most of us would really need to know more details before throwing any kind of numbers out there.
