As far as what i was able to find...the stat reduction of curses is a numerical penalty effect and not ability damage or drain. so yes, you would be effected by that as far as i know.
Bestow Curse doesn't cause ability damage or drain, its wording says "decreases 1 ability score by 6". So technically it would still affect you. What I'm curious about is how you're immune to ability damage/drain in the first place?
2 If a continuous item has an effect based on a spell with a duration measured in rounds, multiply the cost by 4. If the duration of the spell is 1 minute/level, multiply the cost by 2, and if the duration is 10 minutes/level, multiply the cost by 1.5. If the spell has a 24-hour duration or greater, divide the cost in half.
Bestow Curse doesn't cause ability damage or drain, its wording says "decreases 1 ability score by 6". So technically it would still affect you. What I'm curious about is how you're immune to ability damage/drain in the first place?
all undead are (assuming the OP is a vampire from the title of the thread)
2 If a continuous item has an effect based on a spell with a duration measured in rounds, multiply the cost by 4. If the duration of the spell is 1 minute/level, multiply the cost by 2, and if the duration is 10 minutes/level, multiply the cost by 1.5. If the spell has a 24-hour duration or greater, divide the cost in half.
Sounds reasonable, but check with your GM as this is a custom item. Compare Lenses of Darkness which give only immunity to light blindness (and do nothing for undead creatures' sunlight vulnerability) and which cost 12,000 gp.
Do note that undead are not immune to all ability damage. They are only immune to ability damage to physical ability scores. They can still take ability damage to mental scores.
Quote:
Not subject to nonlethal damage, ability drain, or energy drain. Immune to damage to its physical ability scores (Constitution, Dexterity, and Strength), as well as to exhaustion and fatigue effects.
Not that it actually matters in this case. Bestow Curse is a penalty, not ability drain or ability damage.