Not really, no. Apple's never released a modular iPhone that could accommodate that kind of functionality.
If you buy your iPhone outright (or your contract has ended), you can always try selling your existing model to help fund the purchase of a new one.
Happily, iPhones have tended to keep their value way longer than competing Android models, so while you shouldn't expect to get full retail price for a second-hand iPhone, you can slice a lot of the cost of a new model away by selling your existing one – as long as you've kept it in good condition.