I have always had good luck at the 1500s. You just have to remember to look around for the best deals. Don't be afraid to take a small notebook and write down prices. Then, when you've covered most of the stands, you can go back and buy what you want from the one with the best price. At the last show (end of Aug), there were several dealers with stipped lowers. I saw several Stag for $99 and a lot of RRA for around $125. J&T Distributing and PK Firearms both carry good parts kits for around $55 and both carry a variety of uppers. PK is an industry partner here so you can find there info in the industry forum. They would probably be willing to work up any custom upper you want and bring it to the show if you call them a couple weeks in advance.
Yes you could get what you want online, but then you have to mess with the FFL transfer fees. Face to face is always my preferance when dealing with recievers.