There are much better cars to buy for $20K than a R34 NA Coupe. If your hell bent on getting an import, there are far better choices that will not only give you a better all round performing car, but allow you to get comprehensive insurance for less.
If I was 17yo and want a performance/sports car id be looking at;
TX3 turbo Laser
S13
R32
VL Turbo
Mitsubishi Galant
early model HSV
RS Liberty
and the list could go on and on and on and on....
That way you are spending $10-15K on a car that will probably already be mildly modded and out handle and out perform a R34 NA Coupe + you will have change to comprehensively insure the bl00dy thing. All of the above mentioned cars are a big step up from a NA VL that you previously owned too.
If it were me however, I wouldnt be spending any more than $5-6K of my own money if I was 17 on red Ps....
$4K+ for comprehensive insurance on a R34 is a true reflection of your driving history and record, I think its reasonable. Pay it and cover your a$$ and everyone else on the road, or dont and run the risk of being way up sh*t creek without a paddle......