Two answers based off two starting assumptions:
(1) Assumption: the minimum quality of teaching at your institution has remained unchanged during this pandemic and moving everything online.
Answer: Take the salary/wage that your institution pays non-tenure track individuals to teach an intro econ (or similar intro course); this may be a lecturers, visiting, or PhD students. If the numbers vary a bit, take the average. Then prorate their semester pay by 12/(6+12)=2/3.
(2) Assumption: online teaching should have a different compensation (e.g., b/c it gives the instructor flexibility to live wherever they want or b/c it is easier/harder).
Answer: take a sample of salaries of econ instructor as online institutions (prior to 2020). Then prorate their semester pay by 12/(6+12)=2/3.
IF I estimate #1 from the subjective info from my previous institution, it would be about $8,500*2/3 = $5,700
IF I estimate #2 from some random googling, it would be about $4,400
Thus depending on your institution, that should give you an upper and lower bound :)