To be honest if you're on a low budget, you may want to consider a medium length gun like a scar, m4, g36 etc, that way you can play indoors and outdoors. Would also work better for you if you're a smaller person.
Although other people seem to have okay experiences with CYMA, every CYMA gun I've owned or fired has broken within the first few hundred rounds. Maybe CYMA hates me.
A good DMR is insanely expensive to build, and even with that you don't have that much more range than any other gun. I've personally spent about $1000 turning my M14 into a viable DMR, and I still haven't gamed it yet.
Guardians of Asgaard - KF32
VFC H&K 416C
VFC KAC SR16 JL Billet SBR
TM FN Five-seveN