BikeInn has Vitoria Barzo and Mezcal in 650b for £25ish.
G2 TNT 2.25″ 27.5″ Barzo & Mezcal pair is about £66 delivered from BikeInn, I don’t think I’ll get a better pair of xc race tyres for less money.
Unless someone else has seen some other bargains?
Edit: Sorry if I wasn’t clear, the tyres are going to be used on an 11 years olds bike and will be used for xc racing. I’m going to pair them up with the Kinesis Sector Gravel wheels as they’re pretty light, cheap and fit his bike.
I’m thinking of building him up a specific bike for this but there aren’t many small lightweight xc frames and sus forks about for a cheap price so so will probably just stick to his Trek Marlin and try to take as much weight off it as I can without breaking the bank.