There is no fee to open a shop or upload designs. You set the commission at how much you want to make per sale.
Zazzle, Wordans, and Cafepress are big sites that get a lot of traffic, much like Redbubble. Oftentimes the reviews for such sites can be misleading because the few people who have poor experiences are the ones who take the time to write reviews for the site, whereas people who were satisfied with the experience don't tend to write reviews. Sites like Wordans and Skreened might be closer to what you're looking for, though Teespring sounds like an excellent way to start.