Oh for the 347859173498672165 time!
You NERF unit because its OVERPOWERED.
You do NOT compensate for the NERF, because it would lead yet again to unit being OVERPOWERED for the COST and we'd be BACK AT STEP ONE.
This is why it is called a NERF and not STAT RELOCATION.
And to picture it better to you:
I don't remember Guard Rifles getting any cost reductions or compensations when button and PTRS were nerfed.
In case of the JT it's a bit tricky. The piercing rounds were the problem. Relic designed the JT as a 290 fuel unit that has this ability. Now, the whole ability was removed. Therefore, the JT has to lose a bit of its fuel price because it just doesn't have the ability anymore.
If Guards would lose their DP-28 because they are too strong, they'd get something as compensation. If DP-28 would lose some DPS because they are too powerful, they'd get nothing as compensation. In both scenarios, Guards were nerfed.
Nerfing the stats never leads to a buff somewhere else - it has always been like that. Removing a complete feature should be compensated.
The JT's stats (like PEN, DMG, ACC) weren't nerfed - the ability was just removed (partly - but the new ability is kinda meh).
A price reduction to 270 seems reasonable IMO. It'd still be the most expensive unit in the game.