Apple made very few changes for this year's MacBook Pro 13. In fact, if you opt for the two Thunderbolt 3 edition, then the Magic Keyboard is essentially the only feature that separates it from last year's model. Both come with Coffee Lake processors and up to 16 GB RAM, all wrapped up in the same chassis. Apple continued to charge US$100 to upgrade from 8 GB to 16 GB of RAM, too.
However, the latter is no longer the case. Over the weekend, Apple quietly doubled that US$100 surcharge for 16 GB of RAM to US$200. This increase has been reflected in other markets, too. Configuring the entry-level model with 16 GB of RAM in the Eurozone now costs €250, for example, instead of the €125 that it did last week. Similarly, it now costs £200 for the same upgrade in the UK.
MacRumors posits that Apple may be passing increased costs onto consumers. However, the price of RAM has not doubled in the last week, let alone month. DRAMeXchange does not point to any spikes in RAM pricing, either. By contrast, the cost of upgrading from 16 GB to 32 GB of RAM on the four Thunderbolt 3 version of the same laptop remains unchanged. Similarly, the price of configuring other Apple products with more LPDDR3 RAM has not been affected, either.
In short, there is no reasonable explanation why Apple has doubled the price of upgrading from 8 GB to 16 GB of RAM. It may be worth pointing out that only US$100 now an Ice Lake MacBook Pro 13 from a comparably-equipped Coffee Lake model. Cynically then, the change in RAM pricing for the entry-level model could be to drive sales of Apple's more expensive SKUs.