The Siace and Poli are fantastic guns, but well into the used car range.
A couple of thoughts. You can easily pick up a Husqavarna model 20 or 51 for well under your limit. I paid much less than that for a 51 that was made around 1949. The Swedes are known for building stout guns.
Here is an example of a 51:
http://www.gunbroker.com/Auction/ViewItem.asp?Item=72912847This is a 20:
http://www.gunbroker.com/Auction/ViewItem.asp?Item=72698405You could also find a Beretta hammer gun for about your upper limit. They are around, just make sure you can look it over well before you buy. Many of them on the market have seen better days. There have been a couple of Mi Val guns floating out there. Stay away from them.
You might also look at a Bernardelli. Another fine Italian maker that has offered hammer guns in the past.
You can also find some nice Belgian or German hammer guns if you look closely. There are a lot of low grade Belgian guns floating around, but if you find a decent one, you will save a lot of money, especially in the smaller gauges. With the German guns, you can broaden your search if you are willing to shoot a 16ga gun. Many of them are very good quality.
If you find a gun and are unsure about, ask here. There are many who will help.
Pete
they should have really "shot themselves in the feet" and list wt. in grams! 
