Magpul BUIS (the proper ones that will run you about $100 for a full set) are considered the low end for iron sights. Not necessarily a bad thing - no need for expensive irons if you're just shooting paper at the range, but you can do better for a bit more money. Do not buy the airsoft ones (branded "Magpul PTS"). They are not durable, and will not maintain zero under the recoil of a real rifle.
For MBUS make sure you are buying from Amazon directly if possible. Sometimes third party resellers ship imitations or mix up the PTS versions with the real ones.
There are however cheap fixed metal sights so look into those - search "fixed iron sight" on Amazon and you'll get a lot of options. Nothing wrong with the carrying handle rear sight and standard A2 style front.
EDIT: Yo I'm bored so I did your work for you!