I prefer steel, as do many here I think.
Even though the cost will be higher than a plastic part it is still quite affordable for anyone who can afford shooting sports as a hobby. Those that have a plastic one installed will have an easy time putting one of these in their rifle and will benefit from its easier reach and compatibilty with the rifle metal.
I suspect a great many plastic Tapco models will show up on the EE soon, so if "cheap" is what you want just wait a little ...
I should know my exact pricing by the end of the week but I am aiming at a retail price between $40 and $50 ... with a bit of luck I may be able to get it just under $40.