The highest price on a gun shouldn't make it the godly gun. If a gun is 900k, it shouldn't be the god of all guns. It should either have a certain niche where it dominates the most, or it's -slightly- better than the rest. Otherwise you'll be getting into the problem Era had with its legendary weapons:
Best RoF
Insanely large clip compared to their counter-part
Lowest freeze possible
Highest damage outside of the Neorifle and Crizen
Amazing spread
Super fast reload
etc.
These guns were unbeatable and cost a good 1.2mil+ as well as being limited. Because of that, anyone doing a raid was usually mowed down by 1 or 2 of these and it completely ruined the entire game until Venom stepped up and removed them, as well as balancing guns so combat would be a bit slower.