My cheapest AR was my first AR, I built it from a Del Ton kit. It cost me 475 dollars plus the price of a lower (I paid 150, but that was before AR lowers were consistently available for 60 dollars or so). It is an A2 clone, so it was complete except for a mag.
Doing it again, I'd have picked something lighter and handier (and all of my subsequent ARs have been), but that wouldn't have made it more expensive.
It's a great rifle, very accurate, very reliable. Having subsequently owned AR-15s and AR-15 parts made by several manufacturers, I'm of the opinion that, short of a premium brand like Bravo, Colt, or similar, the Del Ton stuff is just as nice if not nicer than many of the more popular manufacturers(Spikes, CMMG, RRA, Bushmaster, etc). Properly optioned, the Del Ton rifle will have all of the features of the more expensive rifles, and they have undergone all of the same quality assurance processes (MPI/HP, etc) of the big name manufacturers.
Depending on the configuration you are looking for, you can get a very serviceable NEW AR-15 for $515 plus shipping and transfer, IF you are willing to wait for a stripped lower to go on sale for 49.99. If you can't wait, there are lowers for sale in the 60-80 dollar range pretty much every day, the trick is just checking around and finding who has them in stock.
Mags, optics, and possibly rear sights are not included at that price.
Assembly is something that anyone who can rebuild a carb or detail strip a pistol can handle no sweat.
Right now my only other "real" AR (I've got a dedicated .22 gun too) is a Bravo Company rifle, it was ~900 before I started to add accessories. In it's current configuration, it cost me $1300, and the only thing I'd add to it would be an optic, it's otherwise as close to perfect as a man made contrivance can be.
I seriously love that rifle, I like that rifle so much that I actually wear the hats they sent me. Daily. They're actually pretty decent hats, and they are nice and subdued in color and logo.
IF all you want is a basic plinker, I'd get a Del Ton Dissipator or middy 16 inch kit, if you like a light rifle, get the middy with the light weight barrel, select the 10 dollar option to have an A2 style upper so you don't have to buy a rear sight. Chrome lined or not is up to you, a chrome barrel will last longer and clean easier, while a chrome moly barrel will be more accurate, but be shorter lived. A plain jane M4 stock is fine, but if you want to upgrade, a Magpul CTR is an excellent no-frills stock that locks down more completely and doesn't wobble. The STR is the same thing but with battery storage compartments. Go for the Mil-spec tube, there are more options for a millspec buffer tube than there are for a commercial, and for many people AR buttstocks become somewhat like holsters in that they collect lots of different ones.