IF your opponent play it again, RT has no effect at all. (except 1 turn draw denial and cost)
1 turn draw denial and the cost is a lot!
The point was that RT is not an instant removal since it is not permanent.
Anyways, this card should be compared with cards that negate the attack strength of a creature. Antimatter is the prime example of 100% negation and 100% healing. Insanity is X% negation and X% damage. Damaging the opponent is more valuable than healing so a 100% Insanity would cost more than Antimatter. Insanity is not 100% so it would cost proportionately less.