Whats needed is about £500 for the direct access course and a bit of common road sense and you should pass no problem. If youve had bikes before then you got the basics, so its just applying and adapting that to the road. Very different to driving a car on the road though.
I used to race motocross too and found it pretty straight forward. the theory test often gets many people though. Not the multiple choice as you just go through the book before hand, but its the hazard perception where many people struggle.