Herodotus provides some details on how mummies were made. And a form of mummification was available to all classes of Egyptians. He describes three specific sets of rituals: one each for the nobles/wealthy, the middle class/merchants, and for the peasants. At the high end you have the whole process of organ removal, canoptic jars etc. And at the low end they would simply pump out the blood and then cover the body in natron for 70 days. The family would then wrap the body (or not) as their means allowed.

This means that the vast majority of Egyptians over a period of roughly 3,000 years were mummified. So there were tens of millions of mummies made... maybe even up to 100 million. Population figures for Egypt are of course not exact. Mummification slowly fell out of favor in the early Christian Era. And by 700CE it was gone.

Additionally (and here I am using somewhat questionable stories), there may have been a resurgence in the practice in the 19th century. Apparently some enterprising Egyptians found out that Europeans and Americans would pay well for mummies. And so they started manufacturing new ones, that were then made to look ancient.