The reason payloads are expensive is because launch was expensive. If you're paying $10k/kg to launch your satellite you have to make sure it has a 99.9999999% chance of working when it gets to orbit. But if you lived in a world where you pay $10/kg for that same launch and could schedule another launch the next day to replace a payload that didn't work, your satellite would be much cheaper because you could afford to have it fail.
It would also be cheaper because you could afford more standardization. You could afford to use a standard bus, for example, even if it makes your satellite heavier than it needs to be.
There's a virtuous circle here. Cheaper launches mean cheaper satellites, and cheaper satellites mean more launches as previously un-economic activities start to pencil out.