You DO NOT need to send $ for this achievement.
This is very easy once you obtain the Fractured Ward Guardian. The hard part is that obtaining the Fractured Ward Guardian is somewhat RNG based.
Once you obtain the Fractured Ward Guardian just equip it before battle when selecting the character for the mission. Continue using Fractured Ward on all your character on all missions until achievement pops. It's that simple. The Guardian will do all the work for you.
But how do you obtain the Fractured Ward Guardian?
The Fractured Ward Guardian comes out of Guardian packs you get from the emporium in Shadow Lords mode. There are different Guardian packs of differing value. For this achievement you can use the Fractured Ward Guardian from the least expensive Guardian pack. The quality of the Fractured Ward Guardian does not matter. The cheapest Guardian pack is 500 Gems. You could get extremely lucky and get a Fractured Ward on your 1st pack but more than likely you will have to buy multiple packs and may get doubles of guardians besides the Fractured Ward before finally getting this Guardian.
But how do I get Gems?
You can get Gems by playing Shadow Lords mode or by doing daily log in objectives in Single player and Multiplayer modes. The quickest way is to play Shadow Lords but logging in everyday for the daily rewards adds up over time and not only do you get Gems, you also get KI Gold every few days. You can also use KI Gold to but the Guardian packs.