Wholesalers have it figured out. Good idea finding your own deals. I've found all mine off market, this is what I do.
Before you jump into the game make sure what you are doing is legal. There are a ton of laws regarding auto dialers and rvms and sms blasts. Know the laws! we have a law firm on retainer to keep us and our partners safe since this is all changing so fast. Here's a good place to start.
https://www.ecfr.gov/cgi-bin/text-idx?SID=4be87749...
Now in terms of what not to do. Don't use excel to manage all leads. it's possible, yes. but you're going to run into issues and ain't no body got time for issues! $3k per month is a solid budget to get some hot leads and a good CRM to manage them. Use podio. and then it's just up to you to negotiate and close a deal :)
What I would do is buy a list of property owners, (make sure you get business owner names too), find a good appending service who can give you principle names who own the businesses, owner addresses, and owner phones. Upload all that information into podio and find a phone system that allows you to contact them virtually. Then find some VA's that can manage the outbound and inbound calls and texts. They'll filter all the cold leads, update your crm and you just handle the hot leads from people who actually want to talk.
As far as direct mail, build a relationship with a mailing house and let them send bulk marketing mail for you. They should be able to send mail "all in" for less than $.60 per envelope with a letter. I don't know about postcards because we don't do those. Put a different phone number on your letter so you can track what works best in your crm.
That's a good place to start. Let me know if you have questions!! :)