There are only five (5) cellular companies in Pakistan. Just check their charges and FAQs on their websites. I think all of them had packages which were based on volume of data, so connect disconnect charges were exempted.
Just subscribe to any of the following data package. I would recommend going for weekly or monthly packages unless your usage is very limited.
Charges aksar bohat hi small fonts main likhay hotay hain goor se parhna.