If you are still going with the "extension cord" route, give me the name plate
rating of your dust collector (voltage, HP and FLA) and I will tell you how to
set it up.
The answer will probably start another fight ;-)
If your dust collector is 1HP or less at 240v you can probably use a 14ga cord
.... on that 30a breaker and still be within the code. (using the NEC article
430 rules)