P90/PS90 in 7.62x25. And also costs what it's worth to mfg. it in parts, labor, and markup. I certainly DON'T expect FN, the distributors, or FFL's to take a loss on the product, but it's in no way a $1500 carbine either. Blowback action, and a plastic shell. There is just not much too them. I guess they're trying to recoup their R&D and tooling costs where possible, since they've never sold a massive number as a PDW to anybody's military.
Kel-Tec RFB actually in stock and sold at MSRP. (getting there... however painfully slowly) Same for the PMR. KT has some sort of production bottleneck problem, and they're not letting it out what it is. They don't make any of their stuff fast enough to satisfy demand, save maybe the P11.
Trijicon optics that cost less than the rifles you're putting them on. (No idea if it's market premium, or it really costs that much to make them...)
Top-break revolver that loads from moon clips, and shoots from the bottom barrel. (The new Italian Chiappa Rhino imported by MKS is halfway there. ) Oh, and make it a 9-shot .327 Fed. Mag. integrated light/laser options right in the frame, and make .327 Fed. popular so price/supply isn't an issue.
Make mine a .454Casull, and I'm very interested.... 
Another good one....maybe even one on a MP-5-style receiver.... 
IIRC, some people have made .45-70 Saiga's out of the .410 shotgun model. Does the OAL of .410 vs. .45-70 make that impossible? (Maybe Tromix converted one to .444 Marlin or something... I can't remember)
I have a Kel-Tec Sub9, the metal predecessor to the Sub2000, and I too would love that in 7.62x25. The MP-5/HK-94 clone in 7.62x25 would also be sweeeeeet...
They do sell some Wiselite Sterlings in 7.62x25 BTW... And it's probably pushing 700 ft/lbs out of a 16" barrel.
http://www.jgsales.com/product_info.php/p/sterling-carbine,-7-62x25mm-by-wiselite-backordered-/products_id/4318http://www.jgsales.com/product_info.php/p/sterling-pistol,-7-62x25-cal,-the-colefire-magnum-by-wiselite-/products_id/3940
