In the future I plan to put together a direct mail campaign for deals. 

I'm looking to start a direct mail marketing campaign and was curious as to which zip codes/ areas are you guys are targeting/ investing in.

I would just start a mailer campaign and if I come across a credible deal then just contact a wholesaler I have developed a relationships with.

I'm just starting my mailing campaign, but I did some research before sending them out.  

I focus of multi-media and Mail>Call> Knock campaigns.

The idea of bandit signs that @Jose Flores suggested can work too although I've done bandit signs to market for sellers (usually in weekend campaigns for a variety reasons) and only get a handful of calls.Lastly, since you're likely already driving around a bit in your day job, driving for dollars in the neighborhoods you patrol might not be a bad idea.

I do know of a couple of wholesalers in that area... as far as looking for deals to wholesale yourself, I would do a direct mail campaign of a couple of thousand letters, or if you want to do it for free, you can cold call ads off of craigslist.  

I want to start a SERIOUS marketing campaign focusing primarily on direct mail, but again the money is the issue there.

I was contacted by a seller from my direct mail campaign.

i would spend that money on a marketing campaign so you can get some leads coming in.go on craigslistform some partnerships with other investors. tell them youll do most of the leg work as long as they can help you do a deal and then split profits 5050 or something. if you are low on funds tell them to fund your marketing campaign and youll send them all the leads you get.