Skip steel cable. Learn from commercial fishermen and off-roaders who have mostly all switched to Dyneema winchlines.
Samson Rope Amsteel Blue, Foot | Redden Marine Supply
3/16 is rated to 5,400# and only costs $0.69/lf, and it floats. Probably too slick and small diameter to hold a prussik, but you could probably fit 30-40' on a come-along spool.
You still need a "safety mass" to mitigate the risk of a snap-back. In the event of a failure, even lightweight line could have some terminal hardware--like a biner, pulley, or chunk of frame--come flying toward one end of the other. In the event of line failure, you have almost nil mass to come flying back at you--so in that case, it's much safer than steel. Also no risk of injury from frayed cable bites.