if i have just a regular +1 armor and want ghost touch have to pay enough gold to make it into a +4 armor or enough gold to make it into a +3 armor?
or if i had a regular armor and want ghost touch pay up to a +3 enhancement in gold?
you in theory have to pay the total of +4 but normally you cant "add" enchantments once a weapon or armor is made. in this case all you have to pay is the +3 to have the ghost touch added if the dm will let you.
2. if you had regular armor it must first be +1 in order to add the ghost touch so it would be at a +4 cost. you
RAW you sell the existing magic item for half value and pay half price for crafting the new magic item.
in reality GM fudge crafting rules most of the time to suit their campaign so check with your GM how he wants to do it.
Uhm, wrong.
Adding New AbilitiesSometimes, lack of funds or time make it impossible for a magic item crafter to create the desired item from scratch. Fortunately, it is possible to enhance or build upon an existing magic item. Only time, gold, and the various prerequisites required of the new ability to be added to the magic item restrict the type of additional powers one can place.
The cost to add additional abilities to an item is the same as if the item was not magical, less the value of the original item. Thus, a +1 longsword can be made into a +2 vorpal longsword, with the cost to create it being equal to that of a +2 vorpal sword minus the cost of a +1 longsword.
If the item is one that occupies a specific place on a character's body, the cost of adding any additional ability to that item increases by 50%. For example, if a character adds the power to confer invisibility to her ring of protection +2, the cost of adding this ability is the same as for creating a ring of invisibility multiplied by 1.5.
Pay the difference between the current level (+1) and the new level (+4) and you are golden.