That would depend on a lot of things;

Adwords is just a auction for keywords, if you bid high you get the best position but just like any auction if no one else is buying you'll get keywords cheap. In between that are the minium google want for the word ( a reserve price if you like ).

The key is to know you product and to know your search words. For example I sell an item that most people would term by one two word phase. That's the phase that would cost me the most on adwords. But my experiance of watching my web site logs tells me that most visitors search on another phase and I get that for far less.

You also have to concider the difference between search words and content words. Content words are much cheaper if applied correctlly and although they may not get clicks from people looking to buy. If you place them right with the right keywords they get your domain name in the places where your customers go.

I use adwords in so many ways it's too much to add here works for me but I spend very little compared to come.

Hope that helps.

You can't say. There's no correlation between cost and traffic. If you do your homework it might be possible to get a lot of traffic from $10 worth of adwords campaigns. It also might not be poosible depending on the market you are targeting. Too many variables prevent anyone from saying anything for sure.

As far as converting on the traffic, that all depends on your website. The better it is the more you will convert.

The best way to get people to forums is to register on other forums and post for a while as a normal user. When you have built up a rep you slowly drop in your link as if you've just found it.

This may seem odd behavour but I know for a fact large companies employ people to do this for their products and services. It's part of an increasing move to employ low paid people in places like India to do work that could not possible be viable due to cost in places like the US and the UK.

I would say if you can afford $1 a day give it a go on google adds and also adbrite. I tested that out and got 80 hits in one day for $5 sadly didn't get any orders but that 80 more people who know about my site and with a average of 17% of visitors click "Save to Fav" it could be future orders.

The key to marketing is in you site log files.