What is the cheapest insurance option that meets the $100,000 requirement for an OA visa in Taiwan including COVID-19 coverage?

You can't apply for a Non-OA inside Thailand but you can apply for a Non-O inside Thailand. The Non-O doesn't require insurance. You could enter Thailand on a tourist visa, open a bank account, transfer in 800k baht from overseas then apply for the initial Non-O which gives you 90 days. Before that 90 days expires you apply for a 12 months extension to the Non-O. The only insurance you would need would be for the Thai pass to enter Thailand on the tourist visa.

@John *********

Most people that want an OA get it because they don't have to show any money in Thailand and can show the funds in a bank account in their home country.