Can't support this. 85 Slayer is a big milestone for anyone. This would devalue some incentive. To add further to Diva's suggestion, I found this on the 07 Wiki:
"Due to the volatile nature of the kraken tentacle, the abyssal tentacle degrades as it is used. After 10,000 hits with the weapon, it will degrade and consume the abyssal whip, leaving the player with only the kraken tentacle. If the player has a full inventory, the kraken tentacle will be left equipped in the weapon slot, useless and invisible. Players can combine the charges of two abyssal tentacles. One fully charged abyssal tentacle is worth 10,000 charges, and the maximum one can be charged to, through adding additional abyssal tentacles, is 20,000 charges. This action will destroy the other abyssal tentacle, making this action effectively cost a kraken tentacle as well. This feature can be very useful in PvM situations, where players may use hundreds of charges through several boss fights."
As far as price stabilization, nothing is ever set in stone. Free trade is free for a reason, I suppose.