Sagittarius Showdown can be farmed on Hard or Very Hard fairly easily for newer players, allowing them to easily accumulate event items. However, since Anat requires 0 AP to obtain and is a vastly superior summon, and since Sagittarius Bow is only worth using in niche circumstances, the only items most players will find worth buying are the 5 Half Elixirs per month, one per day, and whatever other random purchases you might want.
Strategy
Sagittarius does a lot of damage, but does not multiattack. He gains a LOT of defense from Troposphere, and Astra Horizon deals huge damage and also neuters your charge bars, so you really just want him to not use his Charge Attack at all. Bring a fire Dark Fencer with Rain of Arrows III to gain the time necessary. Pace the first 50% well, so that you push him below 50% on the same turn that he would fill up all his charge diamonds. This means sandbagging Gravity to help waste his 50% trigger. Between Gravity and Stall, you should have 2 turns to either Break him or push him below 25% to waste that trigger as well. Finish Breaking him as necessary, then take it home.
Event Shop
The event shop sells the Sagittarius summon and Wind weapons. Items may restock with higher costs when sold out.