Does "payless" mean "for zero price", and "free" (as in beer)?
I searched the dictionaries but could not find the word.
I also wonder whether "cost-free" means the same.
"Payless" is not a word in standard English, which is why you can't find it in dictionaries. It may have been invented (possibly multiple times) for advertising or marketing purposes, and in those contexts it probably means "free" or "low price".
For example, there is a shoe chain in the US called Payless Shoes (http://payless.com), but the intention of the word in that context is to suggest that you "pay less", not that you pay nothing.
"Cost-free" is also not a standard English construction, but it would be interpreted to mean that something is free.