Putting together a good database will cost you in the neighborhood of $500-$1,500 depending on if you hire a VA. This will get you about 500 good leads that are properly skip traced and include accurate mailing addresses and phone numbers (to include cells).
From there, 500 letters will cost around $400-$600 depending on your mailer (post cards are cheaper but they have very low response rates). Currently, we handwrite our envelopes but print our letter. We like invitation style envelopes because they usually get opened. You'll hit that list 3-4 times within a 2-3 month period of time.
If you do that and spend ~$3,000, you will almost certainly find a deal worth buying.
Here's how the ROI works on that, we spent ~$20,000 on marketing last year and bought 6 parks. The conservative equity in those parks at the moment is roughly $3,000,000. So, it could be said that our marketing returned $150 for every dollar spent. For this reason, we're hoping to exceed $50,000 in marketing this year.