Well I read somewhere a full combat equipped Clipper will take around 200MCr, FDL 120MCr and Python 100MCr I guess that was completely wrong then
Well, the total price of the ship depends on the base price for the ship's hull plus all modules, most of them A-grade usually. You might also want at least military armor for a combat oriented ship, which usually costs roughly as much as the hull.
So the FdL costs 50 mill + 50 mill for military armor, but only like 20 mill for all important modules, because it has only class 5 slots -> 120 mill + weapons
The Clipper costs only 20 mill + 20 mill for military armor, but like 90 mill for modules, because it needs mostly class 6 and 7 modules. -> 130 mill + weapons
The Python costs 50 mill + 50 mill for military armor and again like 100 mill for modules for mostly class 6 and 7 modules -> 200 mill + weapons