OP likely looking for multiple IP's for "SEO" purposes, even though its been said by many search engines that this does not improve SERPs for the most part. IP's don't always come cheap so be ready to pay a little extra for those IP's
You won't find it cheap, IPv4 is less than limited currently, expect to pay each IP around 2$ so 40$ only for your IPs and that's on the same c class. Otherwise SEO hosting different c-class, there still few provider providing them even if it worth nothing its only marketing scheme nowadays, that will be around 5$ per account so around 100$/m for 20 c class IP and thats on the budget level side, most offer you will be able to found will be way more expensive for different c-class IP.