My marketing plan is weak right now, but I send out 50-80 postcards a day (I prepared them the night before).

The first time I had a seller respond to a post card I was a nervous wreck.

For all of you who try direct marketing through yellow letters/postcards what's the success rate?

I find this trick a little creepy, but I have heard of highly targeted mailers where you send a postcard with a picture of their specific house and a message saying...We are real estate investors who are targeting your neighborhood.

I don't have a magic postcard or letter.

They also have an internal publishing tool that can send out post cards or letters on a one-time basis or a schedule.  

I would say the next step would be to send postcards to an area that you are interested in prospecting. 

I want to upload the say, excel list, or add them to a database with a date entered, and link up to some type of direct mail house that knows that:- Each uploaded list will go through a series of 6 different postcards/letters.

It will take you a while to get traction but if sellers are coming to you (inbound) the likelihood they are motivated is much higher compared to you blasting out postcards and yellow letters (outbound). 

I keep my mailing cost down by using post cards.