To be honest, to me, £350 doesnt sound that much.
Not because of routine dentals but because other problems rabbits can have with their teeth. If it's just routine dentals that covers then it could be ok, but if it's other dental related things such as mouth abcesses, infections etc caused by teeth issues, I would say it's not enough. Poppy has cost me an absolute fortune with dental issues and they didn't start until I had had her for at least 18 months, i would say I have spent at least £2000 in the last 2 and a half years and Poppy's teeth problems alone.