Reports (video link) have surfaced that the newest Pokemon TCG expansion, Ultra Prism, is temporarily out of print, with no known time frame on when a reprint might be available. This appears to have driven up the price of booster boxes, at least temporarily, to over $100, while usually for most SM expansions they have been available at roughly $80.
It is unclear if this is an attempt by The Pokémon Company International to prevent further saturation and the downward pressure on prices that the market for recent Pokemon releases has seen. Or, in a more likely scenario, it simply may be a way for them to fix the printing error the Cyrus Prism Star card featured.
More official information will likely be available soon.