How to Add or subtract rows of one columns this example in sql 2014?
OK, so let's rephrase:  


  for each id, if N=1, return price, else, return price for N=1 for the
  same id minus current price.


You can try this ugly:

select *, iif(tt.N = 1, t.price, isnull(tt.price, 0) - t.price)
from my_table t
left join (select * from my_table) tt on t.id = tt.id
where t.N = 1


Or a trendier version using first_value statement (starting from version 2012) and assuming we have, for all id, a row with N=1:

select *, iif(N=1,price, price - first_value(price) over(partition by id order by N) )
from my_table