I've owned rifles from Larue, JP Rifles, H&K, Wilson Combat, FN, and a few custom builds. None have been better than my KAC SR-15s (mod 2) and my SR-25. It's not just the reliability and accuracy, but also the weight, fit, and feel. I realize not all agree, but KAC is my preference and I'm willing to spend a little extra $$$ to have them.
(BTW, the SR-25 was rated the top AR-10 in an extensive test on YouTube uploaded just a few weeks ago: .)
Having said that, KAC parts are scarce and—following the law of supply and demand—typically are expensive when you can find them. Of course, you already know this.
Right now, you can find new SR-15 uppers in 11.5, 14.5, and 16.5 on Gunbroker and a few other auction/private sales site (e.g., AR.com). They run from $1900-2400. I did buy a complete SR-15 back in 2022 for $3200. I probably could sell mine right now for around the same price (or more).
I currently don't buy KAC SR-15 lowers as (1) they are way overpriced ($800 for stripped to $1500-1800 for complete lowers) and (2) because I typically replace most factory lower parts with my own preferred parts (e.g., Geissele trigger, Radian charging handles, Geissele maritime bolt catch, Mission First stock), I'm not paying that much just for a roll mark. I recommend buying an LMT stripped lower (Defender-L or Mars-L) and building it out with your preferred parts. I have an SR-15 with the 3.2 bolt on an LMT Defender-L lower and the fit is excellent!
Building an SR-15 LRP now will be near impossible, as the LRP 18-inch upper has long been discontinued. I think I've seen two LRP uppers for sale on Gunbroker or AR15.com over the last couple of years, and they were well north of $4000. I would love to own an LRP, but I've pretty much given up that quest.
You might find an SR-25 upper for around $4500 ($6500 for 6.5C). Again, I'd go with an LMT or Seekins lower. I was fortunate to find a like new complete SR-25 a couple of years ago for $5000. If you can find them, they go for north of $8000 now.
KAC suppressors are another story. There are two new models—the 7.62 CRS QDC, PRG and the 5.56 CRS QDC, PRT—that are in stock at KAC dealers and for sale on Gunbroker. The sale price is around $1800 each, but I picked up a 5.56 and 7.62 for less on Gunbroker auctions. (Surprisingly, I received ATF approval in 2 days after my form 4 submission!). Haven't had them to the range yet, but reviews are good. Love the Knights QDC system.
Knights plans to sell the new KS-1 5.56 rifle on the civilian market in the next year or two. Right now, the company is busy providing them to the British Royal Marines.
Keep checking at Knights dealers such as Presample Depot, Operation Parts, Freedom Trading, Riflegear, and Rooftop Defense. Get on email in-stock notification lists. When you do, act fast because the part typically is sold out in a few minutes. Also, keep searching on Gunbroker.