For budget players, I've been using this deck to farm Roaring Rex level 30 and 40. The rarest card you need is Nobleman of Crossout as Blue Eyes Ultimate can be replaced with either a strong ritual or fusion monster.
The plan is just destroy anything he summons with Gate Guardian, while using cards to draw into Mei-Kou or Xing Zhen Hu. Use Mei-Kou on Solidarity or Xing on random face downs. Then Secret Pass on Piranha and double Martyr for approx. 18000 damage
My heart stops for a second there. It's not Nobleman of Crossout, it's Nobleman of Extermination. Crossout banishes flip monsters. I thought Konami added this card already and I didn't know about it.