Usually schools are not responsible for training solo events. 經學校報 only means the school is helpful enough to support those students whose instrumental or vocal teachers are not members and are unable to enroll their own students. Teachers with ATCL or above qualifications can register as temporary members, or what they called as "individual members" in Chinese.
It is the responsibility of your private teacher to check out all rules and regulations.
Like my own singing students, I do the training and piano accompanying, and a week before the competition, their schools' music teachers might listen a couple of times (usually giving some general comments e.g. smile, more feeling.... other than technical advice).
The charge varies a lot depending on individual pianist. It can be as low as $200 (that's what I have heard) but as high as over $500. Instrumental teachers should have recommendations.