Convert Image Into 3D Model to use inside an App

I have a finished, front-view image of a stylised human character and simply need it rebuilt as a clean, lightweight 3D asset that I can drop straight into both a mobile app and a web viewer. No redesign or extra flair is necessary—the goal is an accurate reproduction that respects the proportions, colours and overall look already approved.

Here is what I need from you:
• A production-ready, optimised 3D file (OBJ, FBX or another common interchange format you recommend) with sensible topology so it loads quickly on low-power devices.

Budget is $40AUD for the conversion as the character is already designed.