I think the best advice I can give is do your research and figure out your budget, your space and what is closest to what you are satisfied with as a product. Now the closest thing you are going to get to screen print is buying a heat press and ordering plastitol transfers, if you dont want to screen print yourself. Plasitol transfers are basically the same thing as screen printing, as they are transfers that are screen printed. The nice thing with them, is you can apply them as ordered.
Depending on how complex your designs are and how many colors, you might be able to do vinly. If they are only one or two colors and have fairly clean lines, you could cut and apply vinyl.
But you really didnt give many details as far as your space and budget requirements so its hard to say. The two ways I listed above would probably be the lowest in budget to start.
There is dtg and it is awesome for high detail designs with alot of colors. It is a much larger investement too. But its also great for limited space. I myself built my business for a good year, making sure I had a good customer base, and then invested in mine to make sure I could support the cost and make a profit. Its really important to do what fits your particular business plan. There are many ways to go about it from fairly cheap, to a higher budget. Its really what fits your particular situation. Hope this helps
