If your target audience is in the internet media, I think it makes much more sense to apply your advertising to the same medium. The people using your service are likely to be reasonably sophistocated web users, so I can't see outdoor advertising working. Typically these type of people will search for the service or website they are looking for using google or something like that. So maybe you should use Google Adwords, where payment is on a pay-per-click basis and you can set a maximum daily budget. Allows you to keep on top of advertising spend, while getting metrics on effectiveness