Los Angeles-based augmented reality (AR) startup Mira has raised $1.5 million in seed funding from will.i.am, Sequoia Capital, Salesforce CEO Marc Benioff, Jaunt VR founder Jens Christensen and others to a kind of Gear VR headset for iPhone-based AR. The company’s Mira Prism headset can now be pre-ordered for $99.

That’s significantly cheaper than AR headsets from Microsoft and others, for a reason: Mira Prism uses an iPhone to render AR games and experiences, similar to the way Samsung’s Gear VR headset is being powered by a phone that is inserted into the headset itself.

In Mira’s case, the phone renders AR graphics, and then mirrors them onto a translucent visor. The headset also comes with a wireless controller to play games and navigate through experiences, and Mira is using Unity’s video game development tools to give developers a way to easily build games and experiences for its headset.

Finally, Mira has developed a kind of multi-player mode that allows users to join in on games from ordinary iOS devices even if they don’t have a Mira headset of their own. Mira opened up pre-orders for its headset Tuesday, and wants to ship first units to developers this fall, with consumer sales being planned for the holiday season.

Mira isn’t the first company to use this kind of mirroring for a phone-based AR headset.  San Francico-based Seebright introduced a prototype for a similar device all the way back in 2014, and has since developed its own phone-based AR headset.

The downside to these devices is that they depend on the light of the phone display for AR projection, which can be challenging in well-lit environments. What’s more, the way Mira approaches AR on the iPhone is fundamentally incompatible with Apple’s own mobile augmented reality technology.

Apple introduced powerful AR developer tools dubbed ARKit with the latest beta version of iOS, which allow developers to use the iPhone’s camera to localize and map surfaces and objects in a room. An ARKit game can, for example, use the surface of a table as part of the game, with objects falling to the ground if a player moves them too far over the edge. ARKit apps will become available on millions of iPhones when Apple officially releases the next version of iOS later this summer.