Dynamic Price based on user entry

[Aborady]

I've Posted a question in Magento Stack Exchange and some guy gave a convienient Answer but with no explanation

please have a look and provide full explanation 

i'd be thankful

http://magento.stackexchange.com/questions/63383/dynamic-price-based-on-customer-input

[stevenwaugh]

Please check from the following pricing extensions, all allow you to calculate dynamic price bsed on user input and different filters, 

http://www.magentocommerce.com/magento-connect/dynamic-square-foot-pricing-calculator.html

http://www.magentocommerce.com/magento-connect/csv-price-table-matrix-pricing.html

http://www.magentocommerce.com/magento-connect/custom-options-pricing-dynamic-products-pricing.html

[Aborady]

These Extensions are fine and i already looked at them before they dont fulfill the required calculations where the dropdown is defining the price of unit and the fields are used to calculate 

i've achieved that but overriding > Sales > Model > Quote > Item> Abstract.php

i changed some calculations in calcRowTotal() function it worked but i cant apply any coupons o special offers thats why im looking for other solutions 

[KuafuSoft]

rewrite _applyOptionsPrice method in product price model, that way it will be possible to get a custom price in cart as well as return a custom price via Ajax when customers change options in product page(if you want).