The price of a standard Conquest Point item climbs from 1000 CP for rank 1 item up to 56000 CP for rank 10 items. A higher ranked character can always purchase items from lower ranks; someone at rank 10 has access to all the items available from their nation’s guards, when their nation is in first place. (Note that rank 10 CP items are a bit different from the rest: there is a staff available only at rank 10 that costs just 5000 CP, and rank 10 CP items can only be purchased from guards at a characters home city, not from the guards in Jeuno.) Because of the increasing price of CP items, it is a good idea to see how many cabal online alz you will want for higher level equipment, before spending it all on lower rank items or scrolls.
Signets last for multiple hours; the duration of a signet is equal to the characters rank + the National Conquest ranking of their home nation. (The National Conquest ranking of the three main nations can also be seen on the Regional Map.) For example, a rank 3 character whose nation is in second place will have signets that last for 5 hours. Signets can be refreshed at any time by going to one of these guards and getting a new one; the new signets duration will replace whatever time was left on the old signet. There is no penalty for wearing a signet, and no reason not to have one on as much as possible; wearing a signet when killing monsters also allows you to gain crystals, and helps your nation in the National Conquest rankings.