Q: What is the cost of publishing a thesis?
A thesis or dissertation is a product of original research and is a requirement for obtaining your university degree. It involves months and sometimes even years of research, writing and rewriting to complete. However, sadly, though so much of rigorous work goes into your thesis, universities do not formally publish it. Printed copies are kept at the university library and are circulated internally. Some universities require that students publish this final research in peer-reviewed journals prior to being considered eligible to graduate, but many don't.
However, at the end of the day, it is the fruit of your labor and will definitely add value to the existing knowledge in your field. Therefore, you should try to publish your thesis formally so that it has a wide readership. But a thesis cannot be published as is. The best way to publish your thesis is to restructure it into smaller journal articles and publish these in academic journals.
Regarding the cost of publishing, not all journals charge to publish. There are two different publication models: subscription based and open access (OA). If you publish in subscription-based journals, you might have to pay only some nominal charges for color figures etc.
On the other hand, OA journals may charge fees for publishing. These are known as Article Processing Charges(APC) and the amount varies widely across journals. You should first shortlist a few target journals from your field and then check the website of each one to find out whether they charge an APC and how much.