I think Twitter ads are a great place to start. You can get setup with the in under 30 min. You can start with a very low budget. You can start seeing results as early as tomorrow.

To give you an idea, for http://www.BromBone.com we target the followers of just one account. The people who follow this account are very likely to find our service useful. Overtime we will expand to other accounts. We spend just $5 per day, and that will bring us about 20-25 visitors per day, plus a new follower or a retweet every once and a while. Our ads started running within 24 hours of setting up our account.

This probably won't scale well enough to get all the customer you need, but it can give you a starting point. It can allow you to collect some potential customers email addresses so that you can talk to them and figure out what they need. Or maybe no one signs up at all. In that case you need to make some bigger changes.