Your first opportunity to grab this is on Dimension 4, where runs are no longer capped.
If you struggle, get the magic well, sink all of your gold into essence, put that into your Crit or HP relics (with any leftover essence going to Strength) and have another run. The combination of improved relics and better equipment will see you going deeper and deeper.
The Reddit/Steam guide by ᒍOᑌᖇᑎᕮY Oᐯᕮᖇ recommends using a party of Ragezerker (you'll need the VIP soda for this guy), Healer, Thief, Blackmage and Knight for deep runs, and it's definitely the setup I choose.
Note: Always start from Level 1 with the 'zerker, because his buffs stack; do you want to be fighting level 1000 hitting for 100 damage or over 3k? Yes, it takes more time, but you're rewarded with more gear, money and essence.