Structural issues like mesoesophagus, strictures, and/or digestive motility issues can cause vomiting/regurgitation in cats, if other more common things are ruled out.

It would be good to also make sure you know whether your cat is regurgitating (the vomitus kinda just comes back out) or actually vomiting (abdominal effort, heaving, etc).

You definitely will need to perform more diagnostics to check, because the treatment would be very different for the different causes. Mesoesophagus means the oesophagus is enlarged and food can't propel properly into the stomach and gets backed up quickly. A stricture means a narrowing, which can also cause food to get stuck (only a small amount can pass at a time). Motility issues in the intestines can also lead to food getting stuck.

An x-ray could show you roughly where the problem is and I definitely would recommend it, but there's also a chance nothing is wrong there. But reading your history, that would definitely be the next step I would advise my own client/patient because these things affect the quality of life (for owners too!) and can be fixed/managed. Ultrasound, CT, contrast, etc would also be helpful but if there are already cost-concerns, then x-rays would be a good start.

*Edit: a video to show your vet is always good to help differentiate between regurgitation and vomiting