Honestly from my experiences, running 8th scale is actually cheaper then 10th scale for a few reasons:

First, those parts(arms and such, plastic parts) are bigger and stronger, drivetrain is beefier. In a way it is true that 8th is easier to drive due to traction and track width but it is more sensitive on settings a little bit off and you can and will see the difference in handling.

When I first got my MRX3, I bought tons of parts along with it just like the way I run MTX3, and I have the 8th almost a year and the only parts that I have replaced is rear upright and it wasnt damage from crashing it was just a strip screw hole.

Now here comes the best part, tire wear, for some reason tire wear is alot better then 10th scale. Dont ask me why because I dont know! a set of tires last me at least 4~5 weeks at my local track. And after 5 weeks it was still runable at smaller track, rear tire around 72~73mm or so!

Granted initial cost is more if you were to compare with 10th scale, on the engine part, when you first started you dont really need those big buck modified engines stock one is plenty fast! say Novarossi WC21 R1 Kangaroo is already plenty fast! I would say faster then most ppl needed and they are not that expensive, the last time I checked they are like $350~375us.