I will have one or more for each section, so hold on.
These are relatively cheap weapons that perform well at top tiers. I am going to skip melee for gem weapons, as all are expensive but do not perform very well.
Invader-It takes quite a bit of gems to max out and no one uses this. I understand that you might be hesitant. But it is a dominant force when maxed out and is comparable to the Black Mamba(IMO).
Undertaker-185 gems for the second best shotgun in game, gimme that.
Emperor's Servants-255 gems when max, 10 hit kill. It is just inaccurate at range, but is a great backup.
Dual Hawks-6 hit kill for 185 gems(correct me if I am wrong). It is only problematic when it is hard to hit shots.
Reflector-225 gems, almost a 1 hit kill, interchangeable with Laser Bouncer
Wyvern-190 gems, top tier weapon, however requires practice to hit majority of shots.
Honestly, not much here.
Champion Solar Cannon-260 gems-I told you there wasn't much here
Impulse Rifle-Not the greatest, but it will finish off enemies
Minigun Shotgun-Cheap shotgun that does what shotguns do
Dead Star-Since the 15.1.0 update, it has become like the old days.
Elder Force Saber-Honestly, who doesn't have this weapon
Poison Darts-Hard to aim, but if mastered, is great
One Shot-We all saw this coming, didn't we...
Killer Whale-Rocket Jump