Help me value this package:

G27 As New in Box <100 Rounds
3 ANIB Hi Cap Mags, 2w/Sleeves
3 ANIB Std Mags, 2 w/+1 pinky extensions
3 Holsters, 1 Milt Sparks SSII, 1 Galco SOB,
 1 Galco Front Pocket holster.

I'm considering selling as a package and looking to be fair to the buyer(And to me too).

And thanks in advance for all the .89cent offers

Not being a smartass, what it's worth & what you're gonna get are two different things.

A NIB 27 goes for around $475 or so. Used will be $350-400, probably. Mag value always causes dickering as everyone thinks different.

Your gonna get hosed on the holsters. Most gun shops give nothing on holster trade-in with a gun. If someone doesn't want that particular style/brand of holster then they're not gonna buy them, IMO.

Good luck.

I'm thinking I'm just going to put a new barrel in it and keep it.  Can I put a .357 Sig Barrel in it?

Yes, a .357Sig barrel will work ok. I've read, but don't know for certain, that the Glock 31/32/33 have beefed up rails to handle the extra stress on the gun.

But if you're not shooting 200rds a week out of it, that may not be any sort of problem, IMO.