The basic price for whites with an extra for the darks isn't too complicated, You can do that in the price table set up.
Unfortunately you can't easily set up different pricing for different areas - it's been requested - it's done by print area I believe but I can't help with that one having avoided it like the plague
In admin go to decoration processes
enable dtg printing
click on dtg printing / price tables
edit price table
select pricing mode / by colour type
set your prices
The different price for a larger / smaller area is a problem I don't know how to get around.
We have the same issue with some of the oddball embroidery areas we have where we want to charge a premium for particular hooping