Magento – Manage different stocks for different stores/store views in magento 1.9

My site has different stores(city as it is called). I want to manage the stocks for these stores.
i.e.
"Assign/manage different product quantity to each store for the same product."
or in other word (if i am interpreting correctly)
"Change magento inventory settings to store view scope instead of global(default)."

I know that we have a few paid modules available online which incorporate warehouses to solve this issue. But their prices are huge.

Could you please give me some logic to work this out.

Thank you so much in advance.