D&D 3.5 - costs to upgrade existing magic items

[pickin_grinnin]

I'm trying to figure out how much it would cost (at standard rates) to upgrade the following items in D&D 3.5:

Wildshape Leather Armor +2 (bring it up to +5)

Ring of Protection +3 (bring it up to +5)

By "upgrade" I mean getting magician to add pluses to the existing items, if that's possible, rather than selling them and repurchasing the stronger ones.

Thanks!

 

[Richards]

I've always calculated the cost of the original item, calculated the cost of the upgraded item, and paid the difference between the two costs.

Johnathan

 

[pickin_grinnin]

That looks like the best way to do it. Thanks!

 

[Greenfield]

That's pretty much the rule.