Yes, you really can build a modern race car for less than £3.7k and it’s been done many times already. Here is a breakdown of the costs.
Here are some instructions that will give you help during your build.
The club has negotiated some discount codes for members. Details are here, but you must be registered and logged in.
Citroën™ provided parts lists and diagrams. Details are here, but you must be registered and logged in.