$85 is for the box, it might the least expensive TV streaming device that supports 4K TV. I think the 4K Roku box is about $30 more, and the 4K G-TV box lists higher than Fire TV but might sell lower.
After buying the streaming device, you subscribe to the content providers you want. This can sort of be like buying cable a la carte. If you don't want many services it can be $8 a month here, $20 a month there, $99 a year for a third. There is also stuff out there that is pay per view, and content you might buy permanently, for downloading to devices with storage.
If you don't need 4K, just HDTV, the streaming boxes are closer to $50, and the stick devices (Firestick, Roku Stick, Google's Chromecast) are a little cheaper than the boxes, as low as $35.
Apple TV is still just HDTV and sells for $70-$200 dollars depending on storage capacity (because this device connects to Apple services that allow downloads and multiple plays). Roku boxes sell from $50 to $130, some support Amazon Prime.
Before choosing a streaming device, you need to figure out whether you want to just stream real-time (all do this) or download content to play later (not all devices can do this, not all services allow downloads). This decision will help you figure out what content providers you want to subscribe to, then you get the box (or stick) that supports the services you want.
This takes some investigation. Almost everybody's device streams Netflix ($8 going to $10, for movies and old TV series) and Hulu ($8 for recent TV shows but not CBS, they are on Amazon), the pioneer providers.
Amazon devices can buy content from Amazon and will stream from Amazon Prime ($99 a year but also pay per view) but they won't buy content from iTunes. Apple TV will buy from iTunes and supports most of the streaming providers but not Amazon. One of my sisters has both Roku and Apple TV to get stuff from both Amazon and Apple.
That's not the end of it. Google is coming into the market as a content provider, we've not seen how well Google and Amazon will play with each other.
If you want the network programming you currently get from cable, then you might be subscribing to Sling TV ($20 a month). The content provider is actually Dish. You can get a Sling TV app for most streaming devices. Sling will currently give you a Roku 2 free if you subscribe for three months. That's probably the best bargain for breaking free of cable if HDTV is good enough, 4K definition not needed. Roku 2 will stream from Amazon Prime,
Content costs can add up. Sling, Hulu, and Netflix will cost $36 a month, bumping to $51 if you want HBO. Add $99 a year for Amazon Prime to fill it out. There are others you might want to buy separately, e.g. PBS, Showtime, TCM.
Then you have to buy the data bandwidth. I pay $50 an month for 300GB of data at 15-20 MBPS, which is fast enough for smoothly streaming HDTV but might be marginal for consistent delivery of 4K. But I do most of my streaming at a lesser definition, and let the TV scale it up, because at 4-6 hours per day streaming HD I will use up my 300 GB in less than a week. For a lot more money, I can buy a lot more bandwidth, but at my viewing distance for my 32 inch screen, the degraded content looks fine. On a 60-inch class TV, anything less than full HD bandwidth can be a problem up close.
I am using a Chromecast most of the time, controlling it from my iMac (Windows PC and iPad tend to "disconnect" from the streaming device after a while). If I were buying a box for streaming, today I would buy a Roku, so I can control it with a remote, and have the broadest choice of content providers. I would most likely buy a Roku 2, because I don't need the Roku 3 motion sensing on the remote, and don't need a 4K box to feed a 720P HDTV and I won't pay for the bandwidth needed to stream 4K content.
(edit) I just looked through Sling TV's price schedule, and if I bought all the things that I occasionally watch on cable, I would be paying Sling (Dish) about what I pay the cable company. Your mileage may vary.
