Well, a PSoC1 is about 2$ do you need it cheaper?
Probably you did not yet understand the power behind PSoCs, I suggest you to have a look at some of the videos presented here to see how design with PSoCs works.
Kits are a means to an end, that is to develop your own application. In general
they are not meant to be your end product, simply a means to design your end
To answer generally to your "What is the advantage..." questions.
Most of your queries are concerned with development kits (DVK) and you question the relation of price to effort. These DVKs are not ment to be used in the field (built into a running system) but are used as proof-of-concept to enable you to easily build your own prototype and start your design phase from something already running. Due to the fact that the piece count of DVKs is rather small the costs for design, pcb and manufacturing are rather high and the user of the D>VK has to pay for that.
No consider designing your own project WITH a DVK: You get a running working example which you have to integrate and configure to your given requirements: That would be done within an hour. WITHOUT you would have had to program everything yourself, doable but time-consuming. Then the test-phase eating up your time, you need a prototype and so on. I think that could easily consume a week's work, 40 hours. so what is the usual price in your country your boss pays for 39 hours of work? Probably less than the proce for the corresponding development kit.
I started my designs with a PSoC1 DVK and an ICE-Cube (In-Circuit-Emulator) which as I could see today you may get for 330$ which seems to be expensive, but the ICE really DID save me hours.
Today I suggest all PSoC newbees to start with a CYKit-030, -050 or even a -001 and learn about all the capabilities of PSoCs.