Grab a repawning Comet Bloom flower when you are in the Ghost Hideout. Make sure you grab it before crossing the bridge and once you have it leave the hideout.

When you go back to the Ghost Hideout another flower will have respwaned. Take it. Repeat this as many times as you want.

After this take your flowers to Halek Hagar in the Hagar Settlement. He will purchase then for $65 each!

But there's more! You can buy the flowers you just sold him back from him at $43 and then sell them back to him again for $65! Easy money!