New Member Zxr250a1

Hey guys what's good?
I am a new member here from central Queensland Australia, I have a 1990 zxr250 a1 and it has given me almost nothing but grief in the year I've owned it.
Don't get me wrong I love it and it's fun as hell to ride but even with monthly services it's spent more time pulled apart on a stand while I'm looking for parts then it has being ridden.
I don't know much about bikes or even mechanics in general but I'd like to learn a bit about what I'm spending all my money on, 3 months ago I spent $1200 having my valve clearances "redone" (not sure what that entails) and I also had the carbs retuned coming into hotter weather (I'm not completely clueless) but what the mechanics failed to tell me was that I had a massive air leak in my carbs that is what probably caused my problem with the valves in the first place (so my new mechanic says).
The bike has failed a compression test (also according to my new mechanic) reading 30,40,0,0 psi last week after a couple months of sitting in my shed waiting.
So my question after all this is: should I spend the money ($430) on piston rings, head gasket and 16 new valves then throw it all at the mechanic for a rebuild ($2000-$3000)or am I better off looking for a replacement engine? And is the latter even possible to find anymore?