3D printing is extremely more accessible than it was 5 years ago. Most people who go to these craft fairs probably know someone who has, or has access to, a 3D printer. They are available at local libraries in many places. And most importantly, even $200-300 models are very reliable and easier to use now. These businesses are a dime a dozen on Etsy. YouTube has been flooded with videos of people saying “I made X in just one year 3D printing.” Since OP knows how to design they probably should have focused on 3D design and printing services for businesses using engineering materials instead of craft fairs.