Apple's ram and SSD upgrade prices have always been a ripoff. Thats why I miss the days of user upgradable ram and storage. I bought the base 13" MBP Core 2 Duo in 2010 (4GB ram, 250GB HDD) and when I stopped using it, it had a 1TB SSD, and 16GB ram.
At least with the 2014 13" MBP I bought used, I threw in a 512GB SSD shortly after getting it. I did but it with 16GB though.
256GB is enough for most folks though. My mom only uses 170GB right now, and that's how she's always been. My brother also doesn't have a bunch of stuff (like high res music, 4K video, etc) on his MacBook Air either.
The MBA coming with 256GB is fine, but the MBP should start at 512GB imo, and the price difference between 256GB and 512GB shouldn't be more than $100.