American Tactical Imports are now selling a polymer AR-15 lower receiver called the Omni Lower. It has a MSRP of just $50 stripped, and $130 complete (including M4-style stock).
ATI says …
The Omni is a multi-caliber AR15 lower made of reinforced polymer. It is designed after a mil-spec lower and is compatible with most current AR15 lower parts kits, grips and stocks. Made with a high-grade durable polymer material, the Omni can withstand harsh environments as well as everyday wear and tear.
The Omni lower will be available with either a complete finished kit including all lower internal parts and collapsible stock, or as a stripped lower. It has tested reliably with .22, .556, and .410, but is not recommended for higher calibers.
The Omni stripped lower has an MSRP of just $49.95 while the complete finished kit has an MSRP of $129.95. The Omni will be available in a color choice of black or dark earth.