How To Declare Variables Per Row

I know how to set a variable for the entire query, but how do I set one per row?

I have one query which is growing beyond my ability to understand/maintain it. I factor in the sale price of an item based on cost, our markup, shipping & channel fees. The problem is that each one of these has it's own variability. I would like to be able to store inline calculations as a variable such that I can call & add them. Example:

My code currently looks like this

CREATE TABLE #tempPrice (
product NVARCHAR(40)
,price DECIMAL(18,2)
)
insert into #tempPrice (product,price) values('prod1','18.00')

[Code] ....

I would like to be able to work with it this way:

SELECT
product
,price
,Cast(price * 1.1 as decimal(18,2)) as markup
,@markup + 5 as 'markup-and-shipping' -- <-- This factors in all of the previous calculations, plus something new.
FROM #tempPrice

I use Microsoft SQL 2008