$50,000 is really a pretty small amount of investment. by the way you asked the question I am looking at this as only being a $50,000 investment. This will limit your options, but there are a few possibilities.
Here are a few ideas.
#1 - Payday advance store.
Set up a store in a low income neighborhood ( Teens to mid - 20's ). Start a check cashing business where you charge people a fee for a payday advance. I am sure you have heard of these because they are popping up all over. However, you can still find some areas without these where you could get a good footing. The initial investment ( renting a store, advertising, license fees,security, money on hand to start ) would be pretty low. With all the drug addicts in the U.S., there is great profit potential in this industry.
#2. Pawn Shop
Kind of the same idea. They want money now, you charge a hefty fee to provide it.
#3. Check clearance service.
This has very low start up costs. Here is how it works. You contact local businesses that take small checks ( pizza places, etc. ) . You tell them you will guarantee every check they take that bounces. ( For instance if they take a check for $13.21 and it bounces you pay them $13.21 for it ). Stores who dont already have a clearance service will love this because they dont have time to track down some guy for $13.21, so they usually just end up eating it. By using your service, they will never have another bad check again. Either it clears the bank or you cover it. You make money by charging the people who have bounced checks a $20.00 service fee. If the average bad check you buy is $10.00 you only need to get 1/3 of people to pay in order to break even. I would think that 80-85% will pay in the end. You would have to provide the business that you are guarantee checks for with certain rules to help you collect. Common rules are - No starter checks, no checks over $50 ( or any figure you choose ), requiring SS #'s and DL #'s on checks, etc.