Excavation levels on clay ground

[New to this]

Hoping you experienced folk will guide me; how do I research / know what is the 'correct' ground prep for excavating - in this case specifically site access (needs widening considerably as all construction vehicles need to get from single track lane onto site currently entrance <10m wide) and then the 30+m of sub base that will eventually be finished as our new driveway and also the 2m perimeter around the house for scaffolding, and later for pathways?

 

I haven't chosen a final drive surface yet.

 

Two builders have given figures but I can't compare them as one goes down 300mm while the other 400mm (this is to lay geotextile, then hardcore, then Type 1 compacted, in case that makes any difference).  I want to spend the 'most minimum' I can on this without compromising quality; it needs to last once driveway is topped with whatever the final finish is, but I don't want to throw money I don't need at it either.  Ground is very high plasticity clay, if that makes any difference. 

[SimonD]

2 hours ago, New to this said:

Type 1 compacted, i

 

I'm not an expert of ground works but my understanding is that new driveway surfaces need to be permeable which means Type 3 not type 1. With our groundworks company for driveway prep, they specified a compacted finished depth of 200mm of hardcore (type 3) and we are on clay soil.