One of the cheapest form of advertising is to do direct email campaigns, though you have to be careful not to be labeled an email spammer.
So you can always start with your own address book and email friends and relatives and let them know about your site and ask them to pass the messaage on. That is generally the safest way to start an email campaign and not be labeled a spammer.
There are companies out there who will spread your message far and wide. The keys to using them is to check them out thoroughly. You can search for known email spammers, you can also ask to see how it is they collect email addresses. Nothing irritates potential customers more than to get junk email. However many companies get people who sign up to get their email notices and for a fee you can get your site spread far and wide.
Email, like direct mail, marketing is a matter of numbers. As with standard direct mail marketing you need to hit many to get a few responses. The beauty of email marketing is that you can hit so many more than in a few seconds for a fraction of the costs associated with direct mail.
You also get a instant response. Many people check their emails on a regular basis, some check as often as every hour or few minutes. Within a short period of time from the launching of your email message you will know if you have success.
As with all forms of advertisement content and how it is presented is king. If you are not able to write a good ad, have someone else do it. If your thinking of running an email ad run it past several other people before you run the ad. Your looking for the biggest bang for your ad dollar and direct email if done right, can be a valuable tool.
Sparky