I have had success in the past with postcards to homeowners close to their rentals.

If you want a cheaper option than postcards and want to take some massive action (or hire someone else to help you take that massive action), put up at least 25 Bandit Signs a week for a month and see how many leads you get and see what you can convert.

I'm in LA - I'm just starting out - Haven't made any deals - literally sending my 1st postcards this week.

After reading I've decided to go with yellow postcard and it was a huge success. 

For example, an off market seller I was in contact with sent me a picture not too long ago of all the postcards, letters and various pieces of direct mail he had received in about a 6 week time frame... there were about 25 of them!

As @Marc Law suggested, I have been driving around neighborhoods and started sending postcards to apartment buildings that I thought were interesting or looked in disrepair.  

Hello all,I sent out postcards to obituary notices ( I'm not really insensitive) in my area.

I would like to send out post cards instead of yellow letters.

You can do a postcard campaign or something of that sorts but you can also spend a lot of money on something like that with little no return.

Situation: I have postcards made and I don't want to spend a ton of money mailing them out every month.