average gold gain per tick = 50 gold * average multiplier
average gold lost per tick = chance for breakage per tick * percent of cost payed per breakage * equipment cost
average net gold gain per tick = average gold gain per tick - average gold lost per tick
With the most recent patches:
chance for breakage per tick = 0.03 (though low weapon proficiency now increase the chance for weapon breakage)
percent of cost payed per breakage = 0.07
so
average net gold gain per tick = 50 gold * average multiplier - 0.0021 * equipment cost
Using your example,
average net gold gain per tick = 50 gold * 2 - 0.0021 * 6500 gold
average net gold gain per tick = 86.35 gold
It would take you on average 1158 tick to earn 100K gold with 6.5K gold worth of equipment and an average multiplier of 2x.
How many rounds it take to make 1158 tick depends on the game mode. Last time I was recording such values, the average round on the the NA battle servers was 3.25 ticks long, so 1158 ticks would be 356 rounds.