Changing the BCM is a bit of a pain in the 'arris, since it has the immobilizer information in the chips, so just fitting a new one will make the car not start. You would also need to transplant the chips. It may be possible to also repair your old one, depending on whether the person fixing it can find the problem.
Unless you are a soldering world champion/electronics engineer, this will need professional help. Before you pay someone to inspect/repair, it may be worth taking the car to a local auto-electrical place. They may find a bad earth or relay still, and fix it.... costing not much... and if it really, really is a BCM fault, they may know someone local who they recommend/is good at it.
Ralf S.