Re: Help choosing a gun
you have to do some home work for that one, here in Colorado there is a site for just that reason. Craigslist does not allow the selling of firearms.
http://www.njgunforums.com/ Has a forum including a marketplace
Thats all I could find with a quick google search, if your serious about this then start by joining the forums, they can help you much better then we can since they have to live by the same unconstitutional BS you do(my opinion). Its hard for me to give you any good advice bud I just have a hard time understanding that you actually live in the same country I do.
As far as the price of the combo your looking at, it sounds like the going retail value of a shotgun combo, you can add a pistol grip stock I believe but again this COULD be illegal where you live, I just don't know. You need better advice from someone in New Jersey, the best way to get that is from someone in the culture in New Jersey and then verify that by looking up the laws in your state.
By Purchasing a firearm through a face to face private party sale you will likely save money but be forewarned there are those who will not sell to someone they do not know even in the slightest way(the internet), they may ask to see one or more forms of ID. These are to protect the seller as much as the purchaser. The biggest reason to purchase a firearm through a private party is that it is perfectly legal in MOST of the United States but also the government does not know about it.
But you need to research this stuff, your the one who will go to jail not me