Would 2 portable 20,000 BTU ac units cool 1,100 sq feet cheaper than central air heat pump?

In MOST cases, a portable AC unit is LESS efficient than any other type of AC unit.

y is incorrect. ONE larger unit is nearly always more efficient than multiple smaller units with the same total capacity. The reason smaller units are SOMETIMES better is you can turn some of them off when the full capacity isn't needed.

no.

"y"? Does that mean yes?

If they would cool it all depends on construction, load and such. While multiple smaller units are cheaper too operate then one larger unit. I'm not sure how efficient portable units are/would be in this type of scenario. Placement and airflow and such, plus they pump air out of the structure with the way they operate. The makeup air they would be dragging in would lower their overall efficiency/effectiveness.