I believe you should be able to buy 2 rows at a time for the same price. Paying $90 for 54 slots is a tad bit ridiculous. I would be better off just getting /back and multihome so I can get to my chest in 2 seconds and back. I think more people are inclined to buy it if it didn't look like a rip-off. :\
+1 that is way to much would never pay that much for extra inv space Honestly i do have to agree on this one Huge rip off
+1 The point of the feature is to give a little bit more convenient experience to people who donate for the feature. It does not help you make money or give a disadvantage in anyway. It costs $50 to get a full enderchest command that can be carried with you (/eec) and it also comes with several other commands. To get the same amount in /bp it would cost $45. This makes it a waste of $45 if you can just buy extcommands for $50 that comes with /eec and several other useful commands. The only people I can see buying this is the people that are doing it solely to help the server and the people that aren't aware of extcommands, which I believe to be a lower number than the amount of people that would buy this if it didn't cost so much. I believe that if the price is lowered/ more is given, the server will receive more for this harmless feature. tl;dr: Not worth the price when you can buy another feature that does the same plus more for almost the same price. It will also help the server to lower the price.
This is a new feature that came out like... a day/ a few hours ago... PLEASE Give It Some Time To GROW/UPDATE!
I don't believe that there are plans to grow or update the backpacks feature. It's a pretty simple idea and the only thing that it needs changing is the price or the quantity of rows. The fact that a high donating user and several others agreeing with him is saying that it costs too much money for what it is shows that something needs to be changed. Also, it'd be easier to change now rather than later.