Max mains (not including stuff like quests or pets etc.) go for around 100-300m and usually renting is 1-3m an hour so if you see urself renting the main out more than 100 hours its definitely worth it
Don't rent it, you need to set so high prices for it to make you profit before getting banned. I would sell it or make it an gargoyle alt. Only medium requirement is to have an 75+ slayer for gargoyles but after that you can just afk and make easy gp.