Snipers are guaranteed kills no matter anything and operate beyond the range of return fire so its less comparable. They need a screening force but that's more for Los than needing something to sofen the enemy up for them. An unsupported JLI is underwhelming but even an unsupported sniper operates as intended. It will always drop a model no matter what it is or what is around.
280 still is a bit too cheap for that though... they are several times combat efficiency of volks scripts etc and come packed with abilities like boobytrap sprint salvage while also having a vet 1 ability like snipers (medkits)... their inferior model sniping abilities is also vastly offset by the 4 man squad and the increased durability... plus its relatively easy for them to hit vet 5 by bleeding troops other OKW units cannot engage directly...
if you maintain the 70% crit the price has to go above 280...
280 with a reduction to 60% crit as you suggested might be better for balance however...