Here is a tip. If you want to keep your costs low design everything in adobe illustrator. These files are the easiest to scale and we wont have to charge you any art set up fees with vector files. If you are not a designer find one. Craigslist upwork and fiverr has a ton of designers that will work for cheap and make graphics for you in adobe illustrator.
Another Tip. To keep costs down keep print locations down. Every print location you add is literally going to double your print price. I have tried to find ways to lower the cost on multiple locations. It cant be done because each new print location doubles the amount of time it takes to print your shirts.