Hi Samantha-
Thanks for reaching out, and thanks for giving BoldGrid a try in a Cloud WordPress WordPress staging site.
You don’t need to make any purchase for your images to work properly, there’s no difference between the paid and free version with any respect to the way your images are processed.
I know you mentioned that you tried several different image sizes, but I still think that’s the real cause of the blurry issue. I can see a very blurry image on this page, where it’s displayed at 617 x 358 pixels. But, if you look at the source image, it’s really very small (300 x 174 pixels).
Are you able to try replacing those with larger source images? As an aside, I don’t recommend using GIF files for static images, because they’re a lower-quality format and are quite large in filesize compared to a JPG or PNG image.