Considering that that the green member of the M20 cavalier cycle - Cavalier of Thorns - is currently pushing $20, there is probably still room for Cavalier of Flame (planeswalker stamp) to grow, although right now the green Cavalier shows up in 14% of Pioneer decks while the red one is in less than 4%, which means it's going to take a lot more play for Cavalier of Flame (planeswalker stamp) to get anywhere near Cavalier of Thorns price
They certainly belong on a list of best Gruul cards, but the lands and mana rocks are simply necessities that Id rather just give a mention and move on
Sinkhole Surveyor is kinda Bitterblossom, yeah
The Dark Rituals synergize nicely with the artifact core of my collection, so I felt like this was the way to go
Well, every turn, you'll either gain a free Lightning Bolt or a free card
Wizards has an official Amazon account where you can check what the average price for each deck should be