google, google, google....
Found one, but I am not sure if it would be the right zone for you, as it is south west. AERSO (Association Équestre Régionale Sud-Ouest /South-West Regional Equestrian Association)
This show (http://www.aerso.ca/equestran_prize_hj_julaug2011.pdf) under the above area has class fees as $17 each, including tax, plus an office/medical/drug test fee of $25.
In the Trillium circuit here, the kids normally do a schooling round (non judged but still a paid class) plus 3 judged courses. So that would be $110 for the 4 o/f classes and a flat class, plus the admin. So now depending how far the show is will depend on how much trailering is going to cost...$50 to 100, or possibly more. Then at least $50 for coaching.
Then you still have braiding to pay for as well....so $25+.