I'm guessing what you are saying is the CHROMECAST device plugs into the HDMI port of the large TV and talks with any WIFI enabled device like your LAPTOP...
Using it like this is just the same as using a HDMI cable but this is wireless...
The cost will come in when you start downstreaming HDTV signals over the internet to your laptop and then passing up to the big screen using the chromecast device... The downstreaming will eat up a 20GB dataplan each month rather quick I would imagine...
The $35 is a one time cost for the device I am assuming. Seems to me I heard it only works on GOOGLE PLAY or something like that...
I might be interested myself if it works just like a wireless connection between any WIFI enable device and a large screen HDTV set.
Just thinking outloud about what the chromecast unit does...
Roy Ken