ᐅ Garage foundation in the workspace

Hello everyone,
in my house construction project, the basement was completed. This week, the earthworks contractor was supposed to backfill the work area.
Problem: a double garage will be built right next to the house later on. That means we will have a foundation directly in the work area.
Question:
How should I construct the foundation?
The depth of the work area is at least 2.5m (8 feet 2 inches). A foundation with a 2.5m (8 feet 2 inches) height will be quite expensive.
How have you solved this problem?
THANKS for your help.

Fill the working area layer by layer with gravel and compact it up to a height of approximately 1m (3.3 ft) below the top of the foundation. Then you can form the foundation, pour concrete, and afterwards backfill the remaining space.

Today, I spoke with my building inspector. He suggested two solutions:
- Completely fill one side with crushed stone and compact it in layers. Then, build the foundation on top.
- Alternative: foundation, concrete block wall, foundation. A mason quoted me 2200€ for this (foundation, wall 6.5m (21 feet) long, approximately 2.8m (9 feet) high in total) and then an additional two foundations about 40cm (16 inches) high for 900€.
What do you think about the second solution and the price?