I was recently on the Joy on March 5th. I booked last minute so my promo was 150.00 min per person. The cost to prebook was pretty high (110.00 per person for the normal streaming) and both passengers had to buy it. The Premium internet with VPN unlocked was 179pp, which was a huge jump from what I paid in the past, so decided to see what my options onboard were
The internet guy wasn't super consistant/helpful, but by day 6, I had a cheap internet package and some thoughts. When you board on day one, and you go to the log in page for the wifi, they offer you 80.00 per device for the non streaming wifi. This is acceptable to me, especially since when on board they were not forcing everyone in the cabin to buy one. The second day when I talked to the manager, there was no wifi deals, but he did tell me I could get 100.00 off a full weeks package of anything with my 150.00 minutes being exchanged. The premium non streaming wifi was 279.00 per device, so after my discount it would be the 179.00 I saw pre cruise, but again, they were not forcing everyone in cabin to get it. We waited until Day 6 to buy the Premium internet, as my husband just needed to log in for about an hr to check out how fast the premium internet was for future cruises where he may have to work. We paid 39.95 per day for 2 days for 1 device, no discount. You technically could just do it for one day at the end of the cruise for 39.95, but they won't let you just buy one day at the beginning of the cruise, if that makes sense. Also. the 100.00 discount is only for a full week of wifi. All of this stuff isn't really advertised, you have to either look on the wifi log in page or talk to the internet manager.
Hope this is helpful!