I'll throw in on this one just to add another opinion, for what it's worth.
For a long time, back a year or so ago when I had been looking for one, Shorty45s seemed to never come up for auction. I looked for one for months -- literally -- before happening upon one totally by accident at my LGS. No box or papers, and only one mag, but I snapped it up for what was an outrageously good price (though not as good as the one Shorty45Mk2 paid for his!)
Since then, say for the past six months or so, I've started seeing them come up on GB from time to time. Folks definitely are testing the waters of pricing on these, and trying not to leave any money on the table in the process. From what I have seen, and how I evaluated my own pistol when I sold it recently by necessity, a used Shorty 45 (and it doesn't seem to matter if it's the original version or the Mark 2) with a couple of mags and no box, is worth at least $900. That indicates to me that a new-in-box example should be worth at least $1,200.
As Shorty45Mk2 pointed out, with only 640 of these produced, the rarity of this outstanding pistol and the renewing interest in 3rds Gens in general and PC 3rd Gens in particular, means that a collector might pay upwards of $1,500 or so for one, but a shooter might not go that high. Still $1,200 to $1,500 is entirely reasonable, I think.
I also agree with Shorty45Mk2 that buying a brand new one with the intention of shooting it is an expensive proposition, and that waiting to find one that has been fired is much preferable. At the same time -- and this will sound like heresy, but it is my opinion -- a good 4513TSW will do anything that a Shorty 45 will do. Both are wonderful guns, and the cachet of the Shorty 45 is undeniable, but S&W really knew what it was doing with these two pistols.
Gone but not forgotten: Smith and Wesson Shorty 45
It's a lesson that has repeated itself several times in the last year. 
A man's got to know his limitations and I sure as heck know mine. 
