1. how can i reduce fuel consumption on my P10 (1995)
2. can a EFI engine fit in place of the current carburetor engine (cost?)

woooo buddy you dont know your p10 that well do you???

all sr20 motors were fuel injected. and for fixing your gas mileage id say do some of these.
starting with the cheapest

timing
clean out your intake manifold
tire pressure
fuel filter
alignment
plugs
plug wires
distributor