There is no 'hope it will drop'. It WILL drop.
The hype machine is in full effect here.
Once the set has been out for a bit, I imagine the Ultra Ball will go for around $40
I doubt that it would drop to $40 here because as people see the card price dropping, they will naturally start to hoard them due to greed and those big collectors will just stockpile on them before it dips that low.
I want to say it will drop but there is one thing people are forgetting. This Ultra Ball is a secret rare cards as well and there are 14 in total in the set. I feel if the card was just a normal full art then it would drop since you could realistically get it but chances are it will be 1 in every 2 or so cases to maybe get one.
I would like to point out that Hyper Rares and Secret Rares are different Rarities, and Hyper Rare cards are far more common than Secret Rares. (Based on English and Japanese observations).
I think it'll go up when it goes out of print and while it's in print will remain $100 and the pull rates like all SRs appear to be 1 in 3 boxes, there are 14 SR/HRs making the ratios 1 in 42 boxes, 7 cases or 1 in 1512 packs Also, the reason SR UBs are so expensive is because 1. Every deck run 3-4 copies and 2. it's a good investment as UB has never rotated out since it's first appearance in DEX...
Basically: Buy them while you still can
Same reason as comment above, Secret Rares and Hyper Rares are different rarities. There are only 6 "SRs" that have the presumed "1/3 box" ratio making it the same pull rate as the PLF one, 1:432.