Answer: about ten bucks.
I have just had the need for one of these cables and there’s really not a lot of choice when it comes to buying these.
You get two options: Buy the cable with the appropriate male connectors on either side or buy an adapter. I prefer the cable option as I find an adapter just too much of hassle. Besides, you still need to buy the HDMI cable separately.
This Mini DP to HDMI, Rankie 6 Feet Gold Plated Mini DisplayPort cable by Rankie looks like it would do the trick and is my recommendation for a cable of this type. It’s long enough as I find 3 foot cable to be a bit short.
The connectors look to be of good quality as well as the cable itself looks to be well built too.
If you do need an adapter vs a cable then the AmazonBasics Mini DisplayPort (Thunderbolt) to HDMI Adapter will work just fine and it too is under $10.00
My vote though is for the Rankie cable and it is the one I would buy