As others have mentioned, most places have stripped lowers for $99 and you don't really need to spend more because the lower is the least useful part of the gun; it just holds the parts together that do the actual work.
Your basic brackets of complete ARs are as follows:
- $500-$600, cheapest you'll find, all Norinco.
- $600-$800, basic models from Ruger and S&W.
- $800-1000, some other brands, or Ruger/S&W with more options.
- $1000-$1500, the start of the "good" ARs. Bushmaster, Sig now makes a $1099 option.
- $1500-$2000, Better Sig models, and the bulk of the Colt lineup.
- $2000-$3000, "Better than MilSpec" models, Daniel Defense, Noveske, Bravo Company Manufacturing, etc.
- $4000-$5000, Ultra premium like H&K and Knights Armament.
For your first AR you really may want to buy a complete unit so you're not building it part by part and researching everything.
Another option is to start with a cheaper full AR and then gradually replacing all of the parts you want with higher end parts, and then at the end of the process you rebuild the original AR from its parts and either sell that or keep it as a second.
Good luck with your purchase.