Your best bet is to bypass advertising on the mainstream internet sites (search engines) and stick to sites like this. Here are a few ideas:
1) Yahoo will get you a lot of traffic. Pay their $199 fee. I once bribed a friend with a 50 pack of cdr's to get his friend who worked at yahoo to review my site faster. Worth every penny.
2)List with every search other search engine you can find, but don't pay fees, especially pay per click or pay per view fees. There's no guarantee your ad is going to be seen, let alone clicked.
3)Make sure you used the appropriate expires /new content tags so the search engines respider your site on a regular basis.
4)Sneaky part- make up 'dummy' pages. Maybe write a boring article on whatever you're trying to sell. Find as many ways to mention the article on that page as possible. Don't link to that page from your site, but provide a link from that page to the rest of your site. List this page with all the search engines you can. When the someone types in the phrase (say it was 'ar-15 magazines'), your page will be one of the first listed, because you mention ar-15 magazines a lot.
5)Include a link to your web site in your signature. Have everyone you work with do the same. Use it everytime you send an email, post a message to any forum, or post to usenet on rec.guns
6)Sites like ar-15.com is where you should spend most of your banner ad money at. Look into sponsorships with sites like it.
7)This is directed more towards getting the customers who visit to make a purchase, but start up a q&a portion of your website. Make a form for people to send in questions, and post the responses on the web. Keep an archive of it. As you get more advanced, add a search engine to search through the q&a. Why do you want to go through all this trouble? Because you and your company will become an 'expert' in the eyes of potential customers. And they'll be more inclined to buy from someone they believe is an expert.
Plus this could also be indexed by the spiders, giving you more matches for possible web searches.
8)Just a general suggestion, but I'd add something like a 'featured product' on the main page. People like pictures. Change it a couple times a week, or have a script that pulls out a random featured product. Makes your page looks fresh if you get repeat visitors.
9)Is there a publication dedicated to what you sell? Don't ignore regular media - if there's a magazine, buy some space in it. Better yet, if you haven't already, start submitting articles, and be sure if they are printed make sure your web site is mentioned in your story or byline. I used to work for an ISP, and you wouldn't believe how much just seeing a story in the business section would get people calling in and signing up.
The old president of the company worked the media well. Every time a reporter needed a quote on something about the Internet, they'd call him. He became their expert. With every mention, they'd say what company he was with.