Like most Pokmon cards, the value of Koga's Grimer depends on a few consistent factors: its rarity, the printing and finish (regular or foil), its physical condition, and the set it was printed in (Gym Challenge)
If Bandai offers a Pre-release for this set, by Pre-Ordering Wolf Of Friendship Starter Deck [ST-16] you MAY be able to pick-up some, if not all, of your Pre-Order during the Pre-release weekend which is typically 1 week before the actual Release Date (while Pre-release supplies last)
Its made only by commons and upgraded/curated, by a community
Popular Unique Shapes & Their Ideal Use Cases Not sure what shape fits your fundraising theme
Considering Cosmic Eclipse's constant climb in value, it's likely that this card will continue to rise until it hits the $50 mark