Not sure why people are bringing melee up as its like comparing apples to oranges and I'm sure you're aware of the value range brings or else you'd be asking for melee.
i'll nonetheless give you my opinion on the three weapons you specified.
-CalyTrek CR Spirit MK.I
Best bang for the buck out of all three options hands down.
Range= 72.6
Price= around 13-15k (I personally wouldn't pay more than 14k in today's market)
Amp= Dante 1.6k
-MarCorp Kallous-7
Range=73.7
Price= Not sure as I've never been really interested in them but would not pay more than what i'd pay for a spirit.
Amp= in order to have same base dps as spirit+dante you would need an Omegaton A204 Overcharged. I know simple A204s are ~15k and HyperA204~30k so....
An amp of comparable cost would be the A106 and would actually give .007 better eco than spirit+dante, but around ~5 less base dps.
-Assassin R150
Unless you believe dpp is unimportant, I won't even waste my time trying to evaluate this weapon. Skip this one.
In summary, being a long time user of a T8 spirit mk.i i'd highly recommend going for this option. The Eco/range/dps was great for me at that level. Contrary to what others have posted in this thread, I ran that bad boy with 8 damage enhancers all day erry day and still profited
. The only reason i'd pick K-7 over spirit would be that you were interested in upgrading to M83 (huge range and eco) and possibly IMk.II. There really isn't too many ranged options past the spirits as of the date of this posting and the only easily available upgrades such as omegaton bucketful (lvl 55) and DOA (lvl 80) really lack in the range department putting the sniper title to shame. If your looking for value - Spirit. If your looking for a better upgrade path - K7. If your looking to reminisce about the good ol' days - Assassin.