@Tyler Thornton, most new investors can relate to your challenge. It can be difficult to find motivated sellers especially when you are working in a seller's market. However, to make things really work as an investor creating leads (consistently) is the life blood of your business.
Here are my suggestions: First, I agree with @Adrien C. that sending 250 letters a month may not produce the results you are looking for. I would also make sure you plan on following up with each seller 4-6 times during the year. Depending on your market you may have to send 2000 mailers before you get a deal you are looking for. I would also not send a yellow letter on the first mailing. It is costly and on your first mailing you are trying to clean up your list. You will get a bunch of mail back being undeliverable so why waste your money on a yellow letter (I think yellow letters have been way overdone anyways).
I don't know what kind of response rate you are getting but it is very important to track. If you get 3 or so calls a month the marketing is actually working. As far as door knocking, I used to do that as well. It is not an easy gig! Working the preforeclosure market is much different now than it was 10 years ago. Sellers are able to manipulate the system and stay in their house much longer than they could years ago. That could have something to do with your response rate. Also, what are you saying to them? These sellers are typically mad, in denial, and embarrassed. Saying the right or wrong thing coud be the difference between a deal and no deal.
So, where does that leave you? No closer to getting that deal you want so bad! I do applaud your persistence! This is not easy! Here are a few of my opinions:
Generating motivated seller leads
Direct mail - Based on your small sample size you may not see any results for months. Rather than competing with all of the other investors that have a much bigger marketing budget than you have you might want to concentrate on smaller type lists.
Code Violations
Divorce
BK
Evictions
There are a lot more. You can certainly continue to mail to absentee owners as well.
If you are going to do a website (you should) you can now look into Google adwords and SEO. Basically driving online sellers to your website.
Next, work on some of the free but need to use some of your own time type marketing.
Make calls on FSBO and rentals on Craigslist and Zillow.
Place ads online
Drive neighborhoods and look for vacant and distressed homes
Go to garage sales and estate sales and see if the property will soon be sold
The last two suggestions I will give you is based on not knowing your experience. I am not sure what you are looking to do with these leads that are coming in. However, if you know how to structure owner financing, lease options and subject to deals you will be able to provide the sellers with many more options rather than just a lowball cash offer. The more solutions you can provide the better chance you can buy the house!
The last suggestion is to either focus on one area of real estate - finding the deals, finding the buyers or finding the money. If you become good at any of these aspects of real estate you will make money. You might also consider working with another experienced investor in terms of birddogging or finding buyers. That way you can learn first hand what it takes to be successful and make some money along the way.
If you have any addtional questions please pm me! Good luck!