the normal stock cars from Tamiya / Kyosho are good enough for novice, just go to their websites and see which ones are good for off road. for a young kid i would recommend cars like the lunch box, wild willy, these can go off road as well and they do wheelies also. the outer shell is hard so not easy to break, large tyres. the cars only cost around 500-600 so not too expensive.
1/12 R/C Lunch Box Gold Edition
after you know what u want, then go to the shops around mongkok and see which one is selling at the best price.