I'm not an expert but I'll start the ball; the 32 acp model 51s are alot rarer than the 380 acps. Consequently, they are more spendy - I've never seen one in these parts for less than $500 and most are in the $600-800 range. You can get a nice .380, if you are lucky, for $350-450. I'd look on Auction Arms and Gunbroker to see what people are asking for these and do a "completed" auctions search to see what they are auctually selling for. Good luck and please post photos if you get the gun. I'd like to get the .380 version someday.
John