I bought these on Ali Express. A little more powerful than the stm32f103 based boards and about the same price.?
https://m.aliexpress.com/item/4000068998794.html?sellerAdminSeq=225519109&spm=a2g0n.search-amp.list.4000068998794&aff_trace_key=8579aea24a4646feb1a851b17fdee222-1576942774546-07232-UneMJZVf&aff_platform=msite&m_page_id=730amp-RqOvgiasXfkKAyk5bgT4fg1580389041433&browser_id=9c6cfcde4b324ba8b4be400eac8f63ff&is_c=N
