The key restraint is availability. Microsoft says it will make 20 Dell Venue 8's available at its stores on Monday for $99 each. After that the price jumps to $199 (still a deal) for the rest of the day or until the quantities run out.
A similar deal will be available at Microsoft's online store that starts with 100 Dell Venue 8's for the $99 price.
Microsoft's 12 days of deals promo, that promises a unique deal each day, starts on Monday.