You can't get much more targeted than a trade journal. Is there a trade journal related to the content of your website? If not, then is there a trade journal almost related to the content of your website? If not, then is there a trade journal about a topic which people interested in your site would also be interested in? If not, then what the heck is your website about?
Create a list of associated trade journals.
Contact the advertising department for each trade journal in the list for a copy of their "rate card." This will have the cost of placing varying types of ads in the journal. You will want rates for both classifieds and display ads. Some trade journals will charge and arm and a leg for advertising and others will be very reasonable. A cheap ad may reflect low readership and/or poor circulation of the journal. On the other hand a high rate is not necessarily a measure of an effective journal. It can be little more than an indicator of greed and insensitive on the part of the journal.
Create an advertising budget and schedule. You will be doing this for a while and unless you're much better organized than everyone else on the planet you'll need a schedule calendar to help you avoid missing those all important placement deadlines.
When placing an ad in a journal many mail-order houses will have a Department A for one magazine and a Department B or another. All by way of tracking referrals from an ad. If the ad produces keep it. If an ad doesn't produce consider dumping it.
But, how do you put a Department A in a webpage? Easy. Create an entrance page for each ad. Don't link to this page from anywhere else on the web. That way any direct hits on this page will partially reflect the success of the ad. You can't be sure it will reflect the full success of the ad. The reason for this is many folks when presented with inputing a URL from a written ad will stop after putting in the ".com" part and go to the top of your site. Hence an ad may in fact be pulling but you won't necessarily see a counter result on the target page.
This smearing of ad results can partially be compensated for with a "coupon" or "give-a-way". In your ad you can include something such as "Be sure to input your entry code DA-73616 for your chance to win" or "Be sure to include your discount code DA-47323 when you order online." In either case you can track the special code to determine which magazine ads are pulling and which are not.