Last summer, ours was $10. It was an adult-youth doubles league.
Like all other leagues, it varies significantly. If there are a lot of high-level bowlers in your area that are interested in a big money league (well, as big as a summer league will get), then $25+ is not outrageous. If not, then it may be more in line with regular league prices.
There's nothing about it being a Sport league or a PBAX league that would make it more inherently costly. The house may raise lineage for that league and you may have to pay extra to cover the cost of pulling tape every week. And you'll have to pay for a Sport Bowling membership if the league actually is sanctioned as a Sport league.
But there's no standard for the price just because it's a Sport or PBAX league.
SH