could of course not pay for a full mummification. I´m not sure but I think there were some simpler means of the process for those with lesser means. Even a stela wasn´t something everyone could afford so simple burials in sand etc would have to do.
Burning the body would mean it was destroyed and one´s chances to live in the Afterlife along with it.
Timeline for how mummification developed - I guess you would like to have when this or that practice started respectively faded out. I´ve never seen a short handy list for that and I don´t know the ins and outs of it really well. Though very great changes did not relly occur during this long practice. Anyone want to take up the challenge of looking into this? :-)