Next week, Apple Inc. is reportedly going to introduce its new iPhone 6 on Sept. 9. So if you have an older iPhone, what's it worth? According to Bellevue-based Outerwall, it depends on what model you have. Outerwall's ecoATM kiosks buy old cell phones, and right now, old iPhone prices are: — Up to $260 for iPhone 5S; — Up to $300 for iPad Air; — Up to $140 for iPhone 5C; — Up to $160 for iPhone 5; — and up to $90 for iPhone 4S. Outerwall and ecoATM said prices are determined by…