I've purchased several heat treated Polish receiver blanks from Cameron "The Dark Knight" Childers, and also recommend him.
The heat treated receivers from Childers guns are available with heat treated and hardened genuine Polish lower rails that are ready to weld in, and since the blanks I have are for the AKM rifle, the extractor tip will have to be shortened some.
Cameron also offers these receivers as finished receivers with the lower rails installed, proper trigger group, center support, and selector/safety lever holes drilled, and the upper rails and mag well trimmed down and fitted as necessary. Of course, these have to go through an 01 FFL since they are legally considered a firearm. Trunnion holes are not drilled, as these are best done to match the actual holes in the trunnions being used with the receiver.
So with the finished receiver (as with one you finish yourself), you are basically getting about the same thing as an NDS receiver, except the receiver and rails are actual European former Comblock production, although the receiver counts as a U.S. made part for the "kiss the federal azz, suck the federal dikk" 922(r) bullspit nonsense.
Why don't you heat treat the rails yourself and save some money? If you have an accetaleen (?) welding set up you can heat treat them yourself. Use a medium tip and a pair of long nose pliers. Get the rails red hot and drop them into either some thin oil or just some water. Then take a wire brush and clean off all the flacky stuff left behind. Then you have to aneal the rails so they are not so brittle but still heat treated. To do that you drop the rails in some sort of can, coffee can etc. fill the bottom of the can with brake fluid until it covers the rails. With a BBQ lighter or a long match, set the brake fluid on fire. Obviously, you want to do this outside somewhere safe. Let the brake fluid slowly burn down until it is out. After the rails cool, you are done. Again clean them off with a wire brush. Now they are ready to spot weld in place.
I got my receiver shells and rails back from Childers Guns today, and they look great. It was a pleasure to do business with Cameron, he was very helpful and polite over the phone and even saw that one of my rails that I sent was bent and after heat treating it was worse, so he sent me a set of Polish rails at no additional charge. Thanks everyone for recommending him.