Nakate, great finding.  Could you please provide the link for these values?  Just reposting your values since we could not see them (I only could see them just when replying from your message box).

0.1micron
Condition : 99.99% Gamma Alumina powder.

20 g  CAD 306.00

50 g CAD 422.00

100g  CAD 553.00

200g CAD 739.00

  Gamma  Size  
    0.1 mm
    Price  
  kg $  
  0.02  $              306  
  0.05  $              422  
  0.1  $              553  
  0.2  $              739  
Extrapolated 0.5  $           1,454  
y = 2327.7x + 289.69 1  $           2,617  
R² = 0.9772 10  $         23,567  
  100  $       233,060  
1 ton 1000  $    2,327,990  
  Volume discount    
  75%  $     1,745,992  
   $ per ton  $        581,997  


Even assuming 75% discount for large qty (dividing price by 4), we are still getting a stunning $580,000+ per ton.  So even at 4N, depending on the granulometry/size and crystallography, price can be extremely high.

White Paper mentions average price of $50,000 per ton for 4N high-purity alumina, but also mentions price can be higher for specific characteristics.