Economically speaking, does it make more sense for me to buy a 1 ply 1000 sheet of toiler paper or 2 ply 500 sheet?
I guess it would depend on the prices of each roll and your TP usage habits.
Studies show that each person has his/her own length of tp they use. So the one ply should last twice as long. YMMV.
The Perfect Master, as one might suppose, has tackled this one. I’ll try to find it and link to it within five minutes of submitting this. For the nonce, though, the answer was that 1.33 single-ply squares (approximately) tended, on average, to possess the utility of 1 double-ply square. Maybe it was 1.66.
Anyway, the upshot was that when Mr 2-ply was replacing a roll, Mr. 1-ply still had either 335 or 170 sheets left…
ETA: HA! Found it.
I will concede, however, that I did not accurately relate the details of the results of the research.
It may make sense but, as far as I’m concerned, life is too short to drink cheap booze or use economical arse wipe.
Cottonelle for me please. 
It’s a question of whether or not you want to wash your hand or not. 
Amen! :o
As my son says: No John Wayne* toilet paper for me!
*rough and tough, and won’t take any shit off anyone.