MAIN question is
if you are really 100% sure that your problem is actually the electronic immobilizer!
So - first of all - start the self diagnosis and check what kind of error this shows to you.
If the immobilizer is really your prob, the little display (in the speedo) shows the error C42.
For error "C42"
I called my brother on the phone and he told me three options / ways.
(As far as I know, he is one of only 3 private mechanics here in Germany who really know this "kind of work" and perhaps you luckily can find an equal private.)
Way 1. - You can finally flash the electronic immobilizer out of the Gen2 ECU via PC & interface.
After that, the ECU never "asks" again for special, coded keys and the ignition lock function of the Gen2 corresponds to that of the Gen1 from now on.
Costs if privately made around 100 € plus shipping.
Way 2. - If you still have a correctly working key with which you can still start Gen2, but all other keys - old & original or new - refuse to serve,
you have to! go to a Suzuki specialist workshop to have all keys re-coded there,
by switching the ECU "electronically" into a very special "key flash" mode.
This mode then causes the control unit to assign a completely NEW CODE to the originally still working key AND to all other keys that you also want to have re-encoded, which means that all keys have a new code that the ECU knows and allows ,
That costs - estimated - quite easily and gladly 150 - 250 € plus the cost of the new keys
plus the transport costs to bring the Busa to the workshop, because it has to go there.
(Or you can find a "private" mechanic that knows how to re-code the keys - but the Busa must also go there!)
Way 3. - The really BITTER! Path, if there is no working key at all,
and the electronic immobilizer should remain active,
is then the mega expensive replacement of ECU, ignition lock (don't forget the tank and seat - locks) and keys for brand new - estimated - around 1,500 - 2,000 € plus the assembly costs - the safest in the specialist workshop.
Way 3b. - To possible "bargain hunters":
Even used, the ECU, ignition lock and key are still around 800 € (don't forget the tank and seat - locks)!
(Have a look to the "Bay" incl. the uncertainty whether the "new" bought parts really work!)
All here remarked "costs"
are german costs