You'll have to pay extra if you find a Beretta 81 in .32 ACP. They are rare and priced as such when they come up.
I looked over on Wikipedia.com. Here is the ballistic info on the .32 ACP vs. .380.
.32 ACP (71 grain) FMJ- 1043 fps- 177 ft-lbf
.380 ACP (90 grain) FMJ- 1000 fps- 200 ft-lbf
Why not just get the model 84 in .380? It holds 13 +1 (1 round more than the 81 which holds 12 + 1 of .32 ACP), has about the same bullet performance, is much, much easier to find, and probably less than half what you'll pay for an 81.
Click
here to see a list of the 84BB's that CDI Sales has on Gunbroker right now. I've actually purchased quite a few 81 Series Berettas from them. If you'll take the time to view each auction, you can find pistols that are barely used. And look at all the auctions. They have 2 or 3 guys that take the pictures and price them. I've found mid-priced pistols in better condition than the highest priced ones.
I bought 1 model 85 (single stack) and 2 model 84s (double stack) that looked nearly new, and got all of them for $350 or less each. I personally recommend the 84BB model. The width of the double stack grip really spreads the recoil over the palm of your hand. Also, the BB versions have grooves on the front and rear of the grip that aid in keeping a firm grip on the pistol.
I actually bought an 84BB with wood grips, thinned the grips down to about half their original thickness, then stippled them to make the grip just slightly thicker than the double stack. So now, I have a lovely blued Beretta pistol that is barely thicker than the single stack version, yet holds 13 + 1 rounds of .380. It is now my daily concealed carry pistol.
This photo shows the 84BB with thinned grips on the left vs. a standard 85 on the right.
This shows the stippling.