Actually, there is a very clever way of doing this and interlinking local businesses and getting them involved as well.

For starters, go ahead and set up your domain, set up a survey on that domain to gather data on interest on the startup and ask what features your users would want. After all, they are the ones who would use it, you want it to be what they want it to be, not what you want.

Open up paint.net , gimp, photoshop or whatever your design choice is and design a flyer. Find a cheap see more print shop to have the flyers printed.
Go to the local shoe store and buy some good sturdy shoes and start hoofin it around town passing out flyers and get with businesses and see if they will pass out your flyers. At the same time you are talking the businesses into passing out the flyers for you, try to find a subtle way to pitch a business deal with them. (Oh and be sure to check in with your local code enforcement and see if you need a permit in order to be out and bout passing out flyers)

I am sure you can think of many other online marketing resources as well.
Although, many people often forget that even with online ventures, good old fashion foot work can reap big rewards as well. Specially since you are targeting your local area.

Good luck on your venture!