I bought the cheapest head unit that allowed bluetooth streaming at Walmart for one of my cars when I was in a pinch... I've had it now for like 6 months, and its awesome.
Streams music perfectly, auto connects, can make calls, also has a great app that lets you control the head unit with your phone or whatever (switch source / volume / etc etc). Simply firing up local music or a streaming service on my phone, then hitting sources switches to BT music or if you want a greater level of control the app gives you that.
Link to the head unit:
Here is the link to the app for full control -