welcome to world of cypress.
I want to know how you want to use ADCs in the application?
Should all 4-8 ADCs to be operated at a time or can you use any ADC to multiplex.
If you are looking for low cost versions using PSOC1/enCoRe devices, please check enCoReIII parts: http://www.cypress.com/?id=177
Using the programmmble options you can multiplex one instance of ADC for upto 4 Analog pins & this device supports two ADC devices along with Fullspeed USB controller.
If you are looking for a device supporting 4-8 ADCs at a time, you need to go with PSOC3/5 devices only.
Let us know if you need any additional help.