Palmetto State Armory has a father's day sale going on now. A complete upper is on sale for $159. You don't need to be 21 to buy the upper.
Watch PSA for sales on their BCG that go as low as $69. Charging handles can be had for less than $25, or your friends may have a stock CH just sitting around. An MBUS rear sight can be had for around $40.
Later when you reach 21 years of age, combine with a PSA complete lower on sale for $129. The whole thing should total less than $450 with no assembly required.
Watch PSA for sales on their BCG that go as low as $69. Charging handles can be had for less than $25, or your friends may have a stock CH just sitting around. An MBUS rear sight can be had for around $40.
Later when you reach 21 years of age, combine with a PSA complete lower on sale for $129. The whole thing should total less than $450 with no assembly required.