Scale and durability
One other aspect is the Scale, an 1:8 scale offroad compared to 1:8 onroad are very different. A 1:8 scale buggy is robust, easy to work on and takes some serious knocks. We dont hear much about 1:10 off road, like it's on road counterpart the tourer it is more intricate, fragile and the scale and tolerances of components need to be up to spec.
Engines are mounted at 90deg in off and onroad as well, starter boxes need adapting etc etc. It['s not a seamless transition in NItro as it is in EP hence EP off roaders would more easily cross to EP on-road than Nitro racers
I started with an 1:8 buggy, didnt take me long to buy road tyres and play, then I found the on-road track and havent touched my 1:8 buggy since.
Expense wise, apart from the benefits of a larger scale, I dont think we'd spend much less off road than on road, it's entirely up to one's personal expectations.
We've raced 1:10 ep off road and you have to spend a few $$ on tyres to make grip etc, it is cheaper in a lot of ways and there's chance attrition gives you a lucky break and a good finish is "FUN" .
The intricacy of on-road, all that power to ground, perfect lines, perfect rounds with no errors, the tuning, clutches, engines, transmissions and chassis and suspension makes the difference for me.
"it's all good..."