Question on magic item creation

[LeifVignirsson]

Yay me! I am such a block head! Can't... figure... out... Brain... hurt!!!

So I am converting the Mud Sorcerer's Ring and it has the ability of casting Earthquake (8th level speel) at a casting level of 14. Multiply that by 2,000 gps and you get your base... that I get...

However, this ability is a once a month type deal... So what modifier do I slap on there? What about 2 weeks or 1 week? Your help is greatly appreciated!

 

[kreynolds]

...at a casting level of 14.

Your caster level can't be that low. The minimum caster level for an 8th level spell is 15.

 

[LeifVignirsson]

Like I said... this is converting... We can put it at 15th level, that's fine, I need to know the modifier... Then I will be more than happy to adjust casting levels

 

[kreynolds]

Well...

...for unlimited charges, 240,000gp...
...for 1/day, 48,000gp...

Now, the fun part. Once a day is 48K. There are 30 days in a month. Once a month would be 8,000gp. Once a tenday (a week) would be 24,000gp. That should be a good starting point for determining your final prices.