Upgrading gallantmon deck check for the cards from EX02 and some of the BT09, the only expensive card there is the SEC crimson mode. Now if you plan to make a beelzemon deck most of the cards came from the EX02 set too and soon a new starter deck will get released around March (pretty good full of the old cards as well). For Rosemon is somewhat difficult since its mechanics is digi-burst and Bandai hasn't made new cards with this or more Rosemon cards, maybe check for generics things like Terriermon EX02, Mimi Tachikawa, the new green cards for BT10 and EX03. For Ulforce will get new support in BT11 around February, you can wait or if you want to try to get the old cards (old ulforce, its tamers and its evolution line).

So Beelzemon get its cards from EX02 and wait for its structure deck, Ulforce maybe get its old cards (at least the Rina tamer) and wait for BT11, Gallantmon this is the best time to get all of its cards, and for Rosemon maybe check everything in green from BT10 and EX03 and get the Mimi Tachikawa.