For a meaningless domain with the least expensive renewal, get a numeric dot xyz. Be sure to verify the registrar has the correct renewal price, they should be around US $1 per year and pick a registrar that offers free whois privacy. Price applies to 6 7 8 9 digit numbers, they are showing current cost $1.22 at porkbun and 85 cents at namecheap
They look totally spammy yet are great for this type of use https://www.youtube.com/watch?v=0dV37t13CSw
These are a specific set of numeric only XYZ with discount fixed pricing including renewals
https://gen.xyz/1111b
working examples 314159 dot xyz 8675309 dot xyz