Plenty of people complaining about very small commissions on 500px. Not worth the time and effort if you ask me, and I would definitely not pay for it. Likes are free to grab elsewhere, so are nanocommissions.
They also seem to have very long review times, so it can take up to weeks or months before your image is accepted for the partner collection, which has pretty strict quality measures. Makes no sense at all to pay for being allowed to upload a fair amount of images, wait weeks for a review only to see that 60% of your batch was denied, and then receive (if you sell) nanocommissions.