KelTec Sub2000 (Glock mag, 9mm) = $399 @ CDNN Sports

[Dynamis]

...and it's still a Keltec.

 

[strongtactics]

Doesn't that require a stamp though? Or is turning a handgun into a carbine legal now?

No stamp needed. Its a carbine, just a folding one.

 

[jwhited]

Doesn't that require a stamp though? Or is turning a handgun into a carbine legal now?

ATF clarified this a few years ago:
http://www.atf.gov/files/regulations-rulings/rulings/atf-rulings/atf-ruling-2011-4.pdf

 

[SSDawg]

Doesn't that require a stamp though? Or is turning a handgun into a carbine legal now?

They don't require a stamp.......the CCU runs around $350-$370 (base version) that's what makes it so attractive (along with the obvious reasons).........check them out.....seems to get very good reviews. http://www.mechtechsys.com/glock.php