It helps to keep an Excel spreadsheet of various components, along with the occasional sale prices.
A high-quality, $1k AR is easily within reach, as long as you don't get greedy. There are some great values out there.
Trigger - You can regularly find the LaRue MBT on sale for $99. From what I've read, it's comparable to a Geissele SSA - the trick is that the $99 price is for a 2-3 month delivery period. That's not a problem when taking your time on the build, like you are.
Upper Receiver - wait for a blemished receivers from Aero Precision. They're a steal, especially if they have an assembled upper; it saves you the trouble of pinning the forward assist. I think they go for something like $70 normally, but if you're patient, you'll have a site-wide sale coincide with a blemished upper. I got mine for $55. I also bought my gas tube, A2 flash hider, and buffer tube with my upper to qualify for free shipping.
Lower Parts Kit - I've seen CMMG kits go on sale at Primary Arms for as low as $25.
Furniture - wait for a sale at Primary Arms. Grip, trigger guard, stock, MBUS sights - I've regularly seen them at 25% off or more.
Faxon regularly has 10% off sales, but they regularly have unadvertised flash sales like the one I just mentioned. If you can get the barrel & gas block for 20% off or more, that's a huge savings.