During the initial run (back in 2006), the wholesale cost of the Wii was just under $200 including $19-20 in assembly costs. They were/are both 90nm process processors. Initially, the price of the CPU was reported as being about $25, the GPU, about $30. The most expensive component was the DVD drive at about $31.
Nintendo is undoubtedly producing them for less currently due to volume purchases of components.
Really no immediate need for smaller/cheaper CPU/GPUs since they cost in the vicinity of $40 or less combined currently.
Kotaku reported the breakdown back in 2006 as follows:
http://kotaku.com/gaming/wii/wii-autopsy-discovers-manufacturing-cost-221736.php
The market value for each is as follows:
Graphics chip: $29.60
CPU: $13.00
DRAM: $7.80
Optical disk drive: $31.00
Power supply: $11.30
Manufacturing cost: $19.50
Cost total: $158.30
Wholesale price: $195.99