Miracast and DLNA

[crazy elf]

So I'm kind of slow with tech developments, my question is what is a Miracast dongle and how does DLNA figure into it. I have a roku steamer and a Mitsubishi 80 inch hdmi television, do I want to buy one, and if I do what is the least expensive option that works well. I'm not cheap but have to count pennies while I am fighting this cancer...