Discount for related products

[adman_9000]

I'm trying to recreate in magento the way the promotions tab works on http://www.wexphotographic.com/buy-sony-cyber-shot-rx100-iii-digital-camera/p1553657

I've tried shopping cart rules and various types of product bundle/group extensions but can't seem to find anything that will do it. Has anyone seen/done anything like that on a magento site?