Why are 2.4 GHz amplifiers costly while RF amplifier IC's are cheap?
I think the best way to have an honest answer about this kind of question is to ask yourself: if you wanted to build these devices yourself, sell them and make a living of it, how much would you want to be paid ?

You have to consider raw material price and how many devices you can build in a day. You will also need some tools, the more advanced your tools are, the bigger your daily production will be. But you will have to buy those tools first. How many $30 amplifiers devices do you need to sell before you can make a pick and place machine profitable?

Long story short, the final price of a product is not just the sum of its components price.