To calculate the total airfares for next year, we need to apply the respective percentage increases to the airfares for this year and sum them up.
For business trips of a thousand miles or less:
20% increase on $9,900 is 0.20 * $9,900 = $1,980.
The new airfare for business trips of a thousand miles or less will be $9,900 + $1,980 = $11,880.
For all other business trips:
10% increase on $13,000 is 0.10 * $13,000 = $1,300.
The new airfare for all other business trips will be $13,000 + $1,300 = $14,300.
Now, we can calculate the total airfares for next year by summing the two amounts:
Total airfares = Airfares for trips of a thousand miles or less + Airfares for all other trips = $11,880 + $14,300 = $26,180
Therefore, the amount that will be spent for airfares next year, according to the accountant's estimate, is $26,180, which corresponds to option (B).