To be honest, I don’t think there are any poor choices now.
Son1 had a Kona Hula. Not the lightest, not great suspension but went around Swinley just fine. His friend had a Specialized Hotrock. Similar quality. The Trek 220 again looks fine. All have aluminium frames and about 50cm of (heavy) front suspension.
Just see what pops up and buy the first that falls within budget. Our Kona was £130 and two years old when I bought it, has done two further boys worth of hard abuse and I passed it onto my nephew last week with new cables.
One last point. 24″ tyres are not great. We ran Schwalbe Land Cruiser as a good on/off-road compromise.