My suggestion is making it so Skyblock Challenges can be reset through an in-game way, like paying 10k SBD or something similar.

Challenges are one of the most important parts of skyblock and without them many items like Dirt and Sand are not accessible at all, so having a limit of 100 on some challenges like Cactus Farmer and Expert Cactus Farmer makes it so players only have a limited amount of Sand and other materials, I myself can not repeat these challenges anymore and have reached the limit on others as well. So adding an in-game way of restarting these challenges will keep items coming to everyone without it being too easy and breaking the economy.