The current costs of the Diamer Basher dam are estimated to be 1450 billion rupees. So far, only 2 Billion rupees has been collected via the fund started by the Supreme Court of Pakistan. On a side note, The Pakistan Army has also donated amounts worth 1 month salaries of soldiers and 2 month salaries of generals and higher post officers.
According to this article by Dawn,
https://www.dawn.com/news/842873/need-for-a-new-paradigm, which is simplified, Pakistan at moment has an estimated 65 million people who are desperately poor, 65 million people who come under the category of lower middle class, 25 million people in upper middle class and 15 million people under the Rich category. These are stats for 170 million people in Pakistan. So, you can deduct the people falling under category of Poor, leaving you with 105 million. It's not complete yet though, as per 2015 to 2017 estimates, 52.5% of the total population of Pakistan is in the age of 0 to 24, which although not necessary, you can consider to be not earning or able to donate. I could not find figures regarding financial status of the population divided under age demographics, so will have to assume that roughly 50% of the 105 million are within the age of 0 to 24. That leaves us with 52.5 million people.
Simple calculation tells us if only each person was to donate a sum of 27000 Rupees from the 52.5 million people, Pakistan would reach the sum of 1450 billion rupees. If the required sum is truly 20% (any source?) then we require 290 Billion Rupees, which means that each person of the 52.5 million people will have to donate Rs 5525.
Now, these are just rough estimates and dumps a lot of stuff that's need to be taken into consideration. Seemingly Rs 5525 per person seems a bit out of reality, many people have their own financial issues, some are simply not concerned, and many are unemployed, many simply are not aware. So, overall, even 20% funding of the dam through public donations seems practically near to impossible let alone completely funding it. The only way public funding will make a considerable and significant impact is if people who are capable of donating go above and beyond what is the bare minimum required of them, in this case Rs 5525 per person for 20% coverage.
In personal opinion, while it is great that such a programme is run to instil the feel of patriotism, and will help the people feel more proud and feel that they have added to a change when the project is initiated and when it is completed, not too much money should not be spent on campaigning for this public donations programme.