I'm looking for recommendations on NAS for home / small office. Main purpose - storage of digital data (documents, photos, movies). Must to have RAID 1 capabilities. Can be enclosure only. Direct connection (access from a smartphone without connection via computer) will be a big plus. Min capacity 1TB (or diskless system) and 2 bays. Budget in a range between $150-$250
I would recommend you take a look at Synology. I have a DS216+ and im very happy with it. Its a bit over your budget.
They also have a "j" version thats $160 here: https://www.amazon.com/Synology-DS216j-NAS-DiskStation/dp/B01BNPT1EG/ref=sr_1_2?s=pc&ie=UTF8&qid=1469742885&sr=1-2&keywords=synology+ds216
and "se" thats even cheaper.
Should be able to do everything you need. If you do install Plex on it, im not sure what performance you will get, because i have the "+" model its a bit more powerful. (you will be able to stream for sure, im not sure about transcoding)
more specs here: https://www.synology.com/en-us/products/DS216j