This applies to all creative fields, not just T-shirt making. It also can help you with your Steemit Blogs :)
With my new creative endeavors, I've been finding more and more awesome stuff that I can have for free or cheap; It allows me to grow my business easier. Whether you design shirts, Logos, Or posters these can help you expand and not be so hard on your wallet.

Creative Market

They have free stuff every week, But also many of the gorgeous graphics and hand painted work is cheap. Some of my best selling stuff has graphics or fonts that I purchased here.
There are also regular sales to save you even more!

Here are the free goods for this week!

Font Squirrel!

This site is FULL Of free fonts that can be used for commercial use! There are so many good ones! This site has probably saved me hundreds of dollars.
Check out Font Squirrel

Open Clip Art!

openclipart.org Is the perfect place for nice little graphics to put on your shirt designs!
There is a lot of lousy stuff, But if you are willing to sort through it, You'll find a lot of hidden gems!

Pixabay!

Ever Wonder where I get the stock photos in my posts? Pixabay is a free site that has a ton of wonderful photos you can use! Also, there is a lot of vector art as well. So if you need graphics for shirts, etc. These are for you!