The answer is $6. 

ELEVEN: 3E + 1L + 1V + 1N = $5.
ONE:    1O + 1N + 1E      = $2.
TWO:    1T + 1W + 1O      = $3.

Each letter in "TWO" is $1 since "O" is in both "TWO" and "ONE". Then, "N" and "E" add up to $1 in the number "ONE" with each of them being 50 cents. Leaving "L" and "V" adding up to $3 in "ELEVEN". Add the prices of the corresponding letters of "TWELVE", and you get $6.