No idea about Karachi market. If you have the old sub, amp and speakers, you can reuse them and save money as audio equipment is getting very expensive.
Otherwise for an efficient but powerful amp I'd recommend soundmagus cs550.4, should be around 16-18k. For sub you can look for the new model of Kenwood, it's a competitor of pioneer 312 and is usually priced better. For components you can find multiple options in the market, all depends on your range but it's easier to find good and original components for a good price compared to amps and subs.
Some wires will have to be cut for amp and speakers to be properly connected. But no door cutting is needed with the regular 6.5 inch component speakers.