Smart key ford focus 2016

[tubara27]

Hello everyone, I bought ford focus 2016 hatchback 2.0
And I would like to get a smart key. The only thing I found online and the price range is 70-110$ and also I found one for 20$ I don't know what is the difference between those two is the cheaper one just a key without anything and does that key has to be activated somehow or those expensive ones are already activated ( but of course I have to set it up on my car) but the major problem is my car does not have push button start is it possible to start the engine with smart key or is just gonna work for doors trunk, alarm.. ?
I assume there is a way to install it but it's probably expensive. I hope you guys will give me some answers I tried to find on google but they just trying to advertise some d*** stuff. Thanks in advance.