Since the fr zam wiki did not have this information I will post it here so that someone can eventually update it.

After the Wildwood derby 1000 is the quest Frost Ridge Invitational, it is the final quest in the demo derby quest line.

Quest: Frost Ridge Invitational

Quest giver: Burt Wrecking' Crewe

Dialog: "Only the best drivers are invited to compete in the Frost Ridge Invitational. When the line up was announced, your name was the first on the list."
"It's a fun, but competitive event. The last driver with a kart still running is deemed the winner!"

Minigame summary: It's time to take your place in the Frost Ridge Invitational! Only the best drivers are invited to compete against each other in this all-or-nothing derby.

Objective: Knock out all other drivers and place 1st in the derby.

Ending dialog: "By winning three special event derbies, you've claimed the Sacred Grove Crash Cup! Congratulations! You earned this!"

Reward: Sacred Grove Crash Cup

ps. I just beat the questline today, a good stragedy to use for the Wildwood derby 1000 quest is to at the very begining of the derby back your kart into the wall and allow the other karts to charge at you then jump before impact so that they run into the wall and you land ontop of them then repeat. After some pratice and patience you should be able to beat this quest.