Starting from Jinan, traveling independently, I want to go to Putuo and Samui. How can I travel the most cost-effectively? The round-trip flight costs over 4,000 yuan, are there any other good ways?

Starting from Jinan, traveling freely, I want to go to Pengpu and Samui. Which is the most cost-effective way? The round trip by plane costs more than 4,000. Is there any other good way?