Quoted:
By the way, I'm interested in the following features:
-flat top (for optics)
-modulate full length hand-guard (15" or so)/low profile has block
-chrome lined barrel
-Ambi fire/safe controls
-anything else you guys think is a "must"
No problem you can absolutely get that on your budget. I built my AR with Magpul MOE furniture for around $615 (including all shipping and FFL charges and a rear sight). The only thing about mine that wouldn't fit your specs is that I don't have a chrome lined barrel: I actually paid MORE to get a Wylde chambered SS target barrel.
Last year, PSA was selling forged alloy lowers for $50 on Black Friday. I expect similar sorts of deal this year. Watch the deal threads here, sign up for email alerts at PSA and other retailers and shop wisely. A couple of hints to save money:
1) Unless you plan on building a number of AR's, go with a completed upper. Otherwise, you'll have to buy a number of specialized tools and probably pay more, especially when you factor in the shipping when you buy the individual parts. Plus, you'll have to worry about things like head spacing.
2) A lower build kit (LPK + stock, buffer, spring and buffer tube) is usually cheaper, especially if you get one on sale,
ETA: didn't see your requirements for a modulate (modular? Do you mean a quad rail?) full-length hand guard and the low profile gas block. Mine has neither and that's going to add to your cost. I still think you should be able to squeak in under your upper limit with smart shopping. Shop sales and know when to combine orders to save on shipping.