The
Riker UL3 should be the cheapest one, if you can find one I wouldn't pay more than
TT+200 for it.
The
Breer M4a is quite rare, there's only 2-3 ingame. My price for it should be arround
TT+300-500 just for rarity, because honestly it's not a very good gun for today's standards. More info
here.
The
Montgomery Anabolic has epic eco, good range but still a bit low dps. The main problem is the high TT but you could find one very decayed. It's a tad better than the Ozpyn LR S1X3, so I guess price should land arround
TT+2k.
And finally, the
Isis LR32 can be a hard one to find and it's the most powerful one. Has the problems of meh eco and very high TT. I would not pay more than
TT+3k for it, you are better grinding with the anabolic imho.
GL