I think what you're not getting is that more magnification won't really help you. For shooting to 5-600m, 6-24 is more than ample. In fact, you don't need a higher magnification for shooting to any distance, really. I run a few 5-25x scopes and the only time I go over 16x is to zero or the odd time to resolve a very small target (like well sub-moa). In fact, depending on the weather conditions, you often can't zoom in much more because mirage gets bad (and these are a high end scopes, like 3 times your budget). The last match I shot, the furthest target was at 1445 yards and you guessed it, I never went above 16x.
See if you can stretch your budget a bit and get used Nightforce SHV 4-14F1 or a Burris XTR2 or Vortex PST 3-15x. When you compare them side by side to your Diamondback Tactical at the same magnification, you'll be surprised how much clearer they are. That's really what makes all the difference. You do get what you pay for and good scopes are expensive, unfortunately. C'est la vie.