The best way to keep marketing costs down is to do it yourself! Ask friends and family to check out your website. Any social event (church, picnics, etc) is a good way to get the "buzz" going on your new business. Create something interesting on your website so that people will talk about it. Consider selling a few unique, strange, hard to find items just for promotional purposes. These items don't have to be directly related to your primary merchandise.
Writing your own press releases is another sound, economical way of getting the word out. Consider preparing a page long, high quality "review" of your website and publish it on free PR sites. Look online for tip on writing press releases that stand out.
Link exchanges with other businesses also works to promote your website in a healthy way. There are many website on the internet that show you how to do this.
Among cheap advertising methods include methods that are not sound and not good for your business. You should definitely not try to send out mass, unsolicited e-mails or purchase bulk e-mailing services. These will quickly ruin the reputation of your business and search engines will make it difficult, if not impossible, for your site to rank well.