you're out of your mind chea.  go see your doctor.

Resistors are the best way to go. The power dissipation is variable but is
always much less than your calculations because the injectors are energized
a small part of the time (low duty cycle.) Same with the power consumption;
if the duty cycle is 5% the total average power is around a watt.

The resistors don't produce a constant voltage on the injectors, but serve
as ballast instead. The injectors are very inductive so the full 12 volts is
initially applied across the injector. As the injector current builds up and
the injector is just being held open more voltage is dropped across the
resistor to prevent cooking the injector. I don't know of any manufacturer
that uses anything other than resistors when using ballasted injectors.

Mike

Pardon me, but a buck converter isn't quite a simple in real life, as
opposed to Wikipedia.  A high power buck converter requires a bunch of
passives (resistors, capacitors, and inductors), and is not cheap,
especially in automotive temperature grades.
They're also NOT instantaneous in operation, and don't like to have
their supply turned on & off thousands of times per minute.
They also dissipate heat (they're "bucking" the incoming power supply),
which needs to go somewhere.

Why don't you just switch to a carburated engine, like an '89 Ford
Fiesta, to go along with your '84 Radio Shack catalog?  They don't need
those power-robbing fuel injectors anyway...  

--Gene