Rogue Amoeba already has a deal where they offer AH and Fission together for $70 ($20 off). That’s a 22% discount.
If you join tidbits.com then most (all?) Rogue Amoeba apps, including those two, are available year-round at 20%-off. TidBits membership starts at $20/yr, and includes additional deals like 6 free months of 1Password for new users, 25% off Bookends, NisusWriter, Drive Genius, PDFPen, PopChar, Capto, Boom3D and Scrivener, $10 off Default Folder, 30% off all TakeControl ebooks, 15% off any Devon Technologies product, 20% off Keyboard Maestro, and more.