You've obtained or made a 3D model and printed it on a 3D print service or perhaps your own 3D printer. Now the question is, "how can I finish it at low cost?" While there are several professional commercial finishing services, they're quite expensive and don't fit the theme here. There are only two reasonable options:
- Print an object that doesn't require finishing by choosing an appropriate material and color. Select an object type that doesn't require a precision surface to avoid polishing.
- Do It Yourself. That's right, roll up your sleeves and do the finishing by hand. You'll need sandpaper and knives to bring the surface to the desired state. You'll need a selection of appropriate paints to colorize your model. Optional Approach: have an interested child do the painting for you. If they do a good job, they might do it just for the fun.