Logical Question about attributes

While storing products in my database i came across this:

I have some products and attributes relates to it,

Few attributes are something like ; No Software (Price: -$200)

it means if somebody selects "No Software" it should deduct "$200" from the total amount just like when we add/select attribute it add the total price. In my situation i want to have frew attributes that should reduce the total price.

I tried storing attributes with -100 or -200 but it prompts a message "Only 0 to 999999 allowed" that means no minus values are allowed.

Can anybody think of any other way to accomplish this ?

start the product  with the lowest price and allow users to add attributes with + values

That i know, but for these particular product, it would not be logical to start with the lowest cost attribute.  The standard product already comes with that feature, it's like out of 100 people 1 dont want this feature that results reduction in price.

Is there any way to insert negative price for an attribute ?

nope, not out of the box

I tried doing this by starting with lowest price but it acts like a calculation bug in respect to attributes

Lets says a product's Market price is $475

The company website gives 2% discount on Market price (act as a benefit of buying products from websit)

So Price or List Price = Market Price - (2% of Market Price ), right ?
[In this situation it comes out to be ; 475 - (475 *2/100) => 465.5 should be the list price]

The subtracted Attribute which i was talking about is like this: (Base model comes with light feature )

No Light = -$160 (means 475 - 160 -> if somebody don't want light feature 160 will be subtracted from the price of the product)

so, $465.5 - $160  => $305.5

So we somebody add the attribute of $160, total price => 305.5 + 160 => 465.5

If i follow this route -> (start the product with the lowest price and allow users to add attributes with + values )

Then i have to reduce the Market price with 160 right ?, means 475 - 160 => $315

Now list price will be 315 - (315 *2/100) => 308.7

Now we somebody add that attribute of $160, the total price comes out to be 308.7 + 160 => 468.7

Now see the difference in figures in bold

Eventually it acts as a calculation bug and customer has to pay few dollars more in that case