What are the cheapest domains for registration and further renewal now? Are there any cons when using cheap domains?
All depends on what the domain name will be, but generally less popular TLDs like .xyz or .shop are $5 or $6 cheaper per year. For the sake of saving $6 it’s better to go for a popular TLD like a .com or .co as it’s more trustworthy for potential visitors.
There aren’t cons to SEO, mainly just the trust factor.