Hi mate,
I would personally say go for the Team Durango 210 RTR kit.
I have recently bought 2 of them for my kids and also I know
Many have bought them at our local club as well.
The reason why I am saying get one is because it's an amazing setup to start with for £164.99 you are getting everything you need to start up except just some battery's and charger.
The car is also upgradable with every option that Team Durango do for the DEX210 so your car can grow with you if wish.
As for spares many local model shops stock parts and there is also the option to
Order spares direct from the Team Durango web site.
On the diff side the RTR comes with a gear diff already fitted so there's no messing about and it will only need to have the gear oil changed once in while.
Here's a link to the Team Durango
Kit page