Buying stun cuffs are expensive in the Fleet store, cost of 600 for 5 - can get 50 for 1,400 crystals in shipments if you save up (each costing 28 crystals).
The other option is to farm nodes. If you use 200 crystals, then this would imply 240 energy, with 24 attempts and with a drop rate of 25%, you would get on average 6 (each costing 33.3 crystals). However, you would get all the XP, coins, and other items that would come with farming the battle.
In my Guild, we are not allowed to ask for stun cuffs in the exchange.