The cost to rent is usually equated in APR, I.e how much curation reward APR you get from renting the HP compared to what the average is, usually it's higher than 8.5% because that's the base-line many can get to without much effort such as delegating to a curation project or trailing an account that votes or simply autovoting.
The idea to rent HP is to use it to promote yourself or a brand or a project, entice people with votes to check yourself out or the project. There should be a "cost" in doing so, if it's cheaper to rent HP than it is to earn curation rewards for it everyone would do it.
Some people rent it just to get connections where they spend most of the rented HP to trade votes with users of similar vote strength, whether they rent or not is a bit irrelevant as they're voting each other only based on interest in votes, not interest in the content or the user.
Greetings, I'm still processing this, I think I understand. Partly, it's about promoting, I understand that. I don't know the percentages and the APRs yet, but I have a general idea: it's not profitable, but if it's profitable for promotion, yes, and if it's profitable for supporting those who need it, they'll believe in your project and support you.
APRs, I still need to assimilate that. I'll keep investigating.
Gracias gracias