Not so for all dates -- it could be quite the opposite.
If all you're after is PF-69 or lower, I agree. However, if you want the perfect 70, it's quite the opposite.
A 2000-S Sac Dollar runs anywhere from $200 to about $500 on ebay. Buying the coins raw and sending them in would probably cost less.
Granted for recent issues (i.e. 2006), it's probably cheaper to get them slabbed rather than send in your own.