Jewelmint is a subscription site that allows you to purchase pieces and sometimes offers MYSTERY BOXES!! Currently they have boxes available starting from $29.99 to $49.99.
The way it works is that once you make a purchase on their site, it considers you a subscriber so you will be charged $29.99 if you do not cancel, purchase, or skip between the 1st and the 5th of the month. If you forget you will be charged and given 1 "credit" which is worth 29.99 towards your next purchase. I recommend just setting yourself a monthly reminder on your calendar if you make a purchase so you remember to skip if that is what you want to do. Otherwise you can also cancel if it is not working out for you. I purchased the 8-piece Summer Mystery Box and am really excited for it to arrive. YAY.