Not sure of all the costs, but my wife and daughter are in one of the trials, and they're each getting paid $1,600 on completion. They also have regular testing visits (not sure how often, though).  Depending on your assumption of how many trials are successful, that might get you a decent part of the way to $10,000 per participant in a successful trial.

A lot of commonly sited drug trial prices are risk adjusted, meaning they take into account the high probability of failure, and are thus many multiples higher than the cost of an actual single trial. 

https://pubmed.ncbi.nlm.nih.gov/26908540/#:~:text=A%20Phase%202%20study%20cost,pain%20and%20anesthesia)%20on%20average. 

"A Phase 2 study cost from US$7.0 million (cardiovascular) to US$19.6 million (hematology), whereas a Phase 3 study cost ranged from US$11.5 million (dermatology) to US$52.9 (pain and anesthesia) on average."

Thus, in reality, clinical trials are not THAT expensive, but they have a high risk of failure. 

What may have made vaccine trials so expensive was the massive number of participants needed to be administered the vaccine and followed to get good data. 43,000 for Pfizer. 

You need to sponsor whole trial centres, pay for the expensive time of doctors, pay for data management and auditing and more. I read a good paper with a breakdown once but was unable to find it for you. There are likely more similar papers.