Since DJI cameras cannot be used on non DJI equipment, the cost of the means to employ one certainly has to be factored into the equation.
Different makers have different prices, that's just the way it is. If people go by spec sheets and individual component price comparisons alone the Inspire cameras look pretty attractive. However, they might be over looking the cost of necessary auxiliary equipment and things like GEO policies that significantly impact their future operating experience.
Each has to decide what they want/need to do and how they want to do it, making product decisions that incorporate those decisions. Choose the product that best suits the users mission requirements. If looking for the least expensive camera rig for amateur use, neither the 520 or the Inspire will satisfy that requirement, regardless of camera selection. Those that desire to play in a higher end market need to accept a higher price of admission will have to be paid to do so.
Making the decision process a little tougher is that DJI will likely cut the price of a basic I2 and P4 significantly the moment the 520 is released. They have been consistent in this practice when the Solo, H, and Autel aircraft were released.