Solution: Cards

HINTS:

To clue letter substitution:

It's significant that only two suits are used.
There are 26 cards in two suits.
It's letter substitution.

To clue the trigrams:

Look for similarities between the words.
The $3 in the introtext is important.

To clue the final step:

Do the trigrams occur more than once?

SOLUTION:

Each card represents a letter.

A of C: A
2 of C: B
3 of C: C
...
K of C: M
A of D: N
2 of D: O
...
Q of D: Y
K of D: Z

Substituting in gives nine nine-letter words:

camcorder
cameraman
dermatome
durometer
expending
matertera
nonending
nonexpert
oysterman

Each of the words can be split up into three trigrams (i.e. cam cor der). Each of the trigrams appears twice in the puzzle, except for cor, dur, and oys. This clues the answer CORDUROYS.