You shouldn’t compare HQPlayer to Roon Bridge. HQPlayer has similar equivalent of it’s own - NAA which doesn’t have extra cost.
HQPlayer itself is equivalent of Roon. But Roon is able to use HQPlayer as it’s player engine.
HQPlayer Embedded is primarily designed for streamer device manufacturers, and you can certainly purchase devices with HQPlayer Embedded built-in. In addition it is offered for DIY streamer builders.
HQPlayer Desktop is generic consumer product.
What comes to GUI, primary GUIs are the control applications such as HQPlayer Client. Embedded is like Roon Server and Client is like Roon Remote.
What comes to price, I think it is one of the least expensive HiFi components. But I don’t know how much you would yourself ask for relative low sales volume product with 25 years of R&D effort.