P-40s hold their value well. Typical sale prices seem to range from $275-$300 - this is about the same (or a little more) as they sold for new. The best place to sell it (and get the best price) would be a Kel-Tec enthusiast forum, like KTOG.org.
50-250
50-250 USD or so depending on condition.
No, they don't.
Best left to a gunsmith
Suggested retail prices Blued Finish $ 318.00 Parkerized Finish $ 361.00 Hard Chrome Finish $ 377.00 AFAIK, there is no sn data published for Kel Tec. You could try calling them.
Kel-Tec was created in 1991.
50-150 usd
100-300 USD
100-300 USD
Yes, the Grendel P-12 is related to Kel-Tec. Kel-Tec originally designed and manufactured the Grendel P-12, a .380 ACP semi-automatic pistol, in the 1990s. The P-12 was later discontinued, but it shares a connection to Kel-Tec through its original production.
It is an inexpensive pistol caliber, foldable, blowback operated carbine- manufactured in Florida.