Jamie.
All depends on how old you are really, if it's your 1st job and you are quite young / still living at home, I can understand your dads comments.
Rc cars are silly expensive. I don't believe for a minute its a 'sport' it is a hobby. Fair play, some people are 'professional' racers but it's all an elegantly engineered marketing ploy to get you to buy product x instead of product y, or persuade you that you need to buy something to remain competitive !
Don't get me wrong I love rc cars, my parents hated it when I was a kid as all they could see was the expense involved.
I returned to the hobby when I could afford it. If I was a young 20 something starting out in life and looking for a mortgage, starting a family / settling down etc then I would sack it off. That's what I did and just got back into it when I could. I've being in and out of the hobby for the last 20 years due to family / kids / doing up my house etc.
I assume, that in these very difficult times your dad is just worried you are wasting your money when it could be used for more important things - if that's the case I'd give him a break !
Alternatively, you could be minted, in that case do what the hell you like
