A part of what makes those M-Blaze discs so expensive is the engineering that goes into them, and the quality of the components. The light cast from them is oriented front and rear, not just an illuminated ring. Yeah, $200 is a lot of money when you're building a bike on a budget, but is $200 for your safety too much to spend?
What if those "cheap eBay knock-offs" contribute to someone behind you, or coming head-on not noticing your intended turn? Instead they cross in front of you, smack into you from behind while you're sitting there. There's no guarantee the MotoGadget lights would prevent the same thing, but they will certainly increase your odds of being seen (at least while turning) due to their intensity day or night.
Indicators and helmets and tires should all be treated with the same priority. Despite their cost, theyre all far less expensive than the cheapest trip to the ER. That's my input. Be safe out there-