Where did you get the 20 grand figure from?
There are numerous bespoke bicycle manufacturers in the United States. If you go all-in on a custom frame build, custom paint job, and super-fancy high-end components you might get your bike a bit over ten grand. Most of those manufacturers only make a few hundred bikes a year or fewer and are pretty high touch (you usually have a personal bike fit and you get the CAD drawings of the frame build for your approval before they start work).
The key point is that the expertise to design and build bikes exists in the Untied States in adequate quantities. But that expertise is all focused on the very high end. You'd need to throw a pile of capital at that expertise to scale up the manufacturing and automate the heck out of the manufacturing process to build bikes at a reasonable price. I think that is doable given time and money. Of course we just vaporized a few trillion dollars so there is going to be less money to go around for that kind of stuff.
On the other hand scaling up bicycle manufacturing in the States is likely to be a better investment than the hundreds of billions of dollars spent on AI in either its LLM form or for self-driving cars. On the other other hand we'd need to do that for every single manufactured good in existence if we want an autarchy and that is likely to be expensive even for a formerly wealthy country.
The dirty secret is that bringing back manufacturing to the States won't bring back manufacturing jobs. Because anything we bring back will be automated at the science-fiction level and scale.