If we have a random bag of 30cm * 40cm * 10cm with all the power banks we can add to it, then it would look like the following:

Making some calculations:

We have the following volume of power banks:

9 * 3 * 4 = 108 power banks

9 * 2 = 18 power banks

Total: 108 + 18 = 126 power banks.

So, in a common / rutinary bag we can trasport 126 power banks.

If each power bank represents:

 20 Ah * 9 v = 180 Wh = 0,180 kWh

 0,180 kWh * 0,11 euros / kWh = 0,0198 €

Then:

 0,0198 € * 126 powerbanks = 2,4948 € ---> Aprox.: 2,50 €

 In conclusion:

 With a bag of 30cm * 40cm * 10cm you can transport 2,50 € of electricity.

If we consider a 20 000 mAh Belkin power bank:

That cost 35 € .

Then: 126 power banks * 35 € each one = 4 410 €

It would cost 4 410 € to have all the needed ones.