There are many factors to consider when determining a home's market value...which is the core of your question. Some essential factors include, location, location, location (of course), the home's condition (can range from move-in ready to light rehab to full gut), schools, crime rate, and the home's status (foreclosure, at auction, standard sale, REO/short sale, etc). This will help you to assess an appropriate target price, location of where you want the home, and the method you will use to uncover possible homes.
Honestly there is not enough room to discuss at any length the numerous ways to find homes. Some people pay thousands to get educated on how to be a real estate investor (like me), others are more passive, read a few books and approach it more like a hobby. Frankly the knowledge you will get by being trained professionally will more than pay for itself in the savings you will realize from the mistakes you will not be making. But assuming you are not looking to invest and want to take the low cost approach using free/public resources, here are some suggestions:
Web sites like Google, and Craigslist, Realtor.com, Zillow.com, and Trulia are good resources. You want to use search terms like "new Paint", "Investor special", "motivated seller", "needs TLC" or similar terms. Once you read a few of the postings, you will uncover new terms. Write them down and search again.
You can drive around target neighborhoods. When you see homes with boarded up windows, abandoned homes, or homes clearly in need of attention, you can go to your county's property tax database (available online), look up the owner and reach out to them asking to purchase. If the owner's address is not the same as the home's address, it may be an absentee owner who would love to unload the property.
Networking is always a good resource. You can find local REIA (Real Estate Investor Association) meetings on Meet-up.com. Find a few and attend. Likely you will meet people trying to sell the very type of properties you are seeking. People known as "wholesalers" do this, and only this, as their job. You want to get on their buyer's list.
So, hopefully this will get you started. If you just do this much, you will be more than busy each week, and the results will come soon. There are paid sites too that are valuable resources, and time savers, but for now I stuck with a few of the "free resources".
aka: Captain Rehab
TEMCO Properties, LLC