Without resorting to these crappy cast receivers (such as Hesse/Blackthorn), the cheapest assembled rifles are going to be the 'bargain bin' rifles from CMMG. If you're looking to build one, Del-Ton had the cheapest complete build kit (minus the lower) at $450.
The NORINCO CQ5.56.
DPMS sell a complete kit for $68.
Try AR15.com Try AR15.com
If it is one of the recent Colt .22LR AR15 rifles, then the answer is no - they are completely different internally.
1959
Yes
The US Army presently uses the M4 carbine, a shorter and much modified version of the Armalite AR15.
Colt has not offered a AR15 in 308
By it's serial number. Go to www.proofhouse.com and under 'long rifles' listing look for AR15 Sporter
@ 40 inches.
Yes
The AR15 series