PictureLife manages pricing based on storage. One of the things I liked about Everpix was that it was $5/mo no limits (AFAIK). If you can figure out a no limit pricing that would be great, it doesn't have to be $5/mo.
I am also a Flickr Pro member. I always thought Flickr+Everpix was a great combination. You can always create a set of apps (desktop/mobile) and have users connect with Flickr accounts to store the pictures. I won't mind paying one time $50-100 for a good Flickr uploader that works more like Everpix.