how much for selling advertising space

It totally depends on your audience and your traffic.  Advertisers should want to know how many unique visitors you have per day, and how many impressions they can expect.  The more demographic information you have about your visitors, the better.  If you're in a niche market, you can make some assumptions about your audience (if your site is mostly about luxury watches, for example, most visitors are likely to have a high household income).  Find your competitors, and compare their ad rates.    You'll want to undercut them initially to gain market share and then start gradually raising your rates.

Also, given the amount of clickthrough fraud, advertisers may be more confident purchasing advertising at a flat weekly or monthly rate.  

I'm currently finding that pay-per-action (commission-based) is worth very little compared to pay-per-click (with AdSense). I strongly recommend you give AdSense a try on a couple of your highest-traffic pages first. If no relevant ads show up (or you only get lame ads for non-sites) then look elsewhere.

Click-throughs are worthless if they don't convert into viable sales, IMHO.