"I'd like to build one on my own, that way it's on nobodby's radar screen."
Unfortunatley you just ruined this for yourself, by posting it on a public forum.
I would have to say that if I were you I would take some community college machining classes and see if it's right for you.
The processes for completing an 80%er aren't super difficult, but you'll at least want some good machining practices. I don't think anyone can build it for you other than Bushmaster, Rock River, et al.
If you're looking for the cheapest way to make an AR, this will not be for you. The cheapest way in my opinion would be to buy a lower of your choice, and a kit to your liking and slap it together. If you're contimplating machining a 80% I'm certain you'de have very little difficulty putting a kit and lower together. Remember there are some aspects of building a 80% that don't involve machining. Anodizing comes to mind.
Now, I'm not trying to talk you out of it. I'm just trying to show you the whole picture. there are people who have completed them with little more than common hand tools:
[url]http://mujahadeenar15a2.tripod.com/[/url]
but it will be much more fun & turn out better with proper tools. check out [url]http://quartz2.cyberstation.net/~dwpaul/bs-home.htm[/url] for an excellent overview/guide to completing an 80%er and decide if it's right for you. Good luck.
Edited to fix link. Just putting a space in front of the http added the extra http, weird.