I've included 12 creatures that can be cast for no more than two mana that either have flying or unblockable, like Triton ShorestalkerTriton Shorestalker, Silent HallcreeperSilent Hallcreeper, and Malcolm, Alluring ScoundrelMalcolm, Alluring Scoundrel
The low-cost characters are fairly vanilla, but there are some more complicated effects in the bigger ones
Raiyuu, Storms Edge If you specifically want to build around samurai as a creature type, Isshin, Two Heavens as One definitely works, though Raiyuu, Storm's Edge is friendlier on the budget
To play a land, just put it from your hand onto the battlefield during either of the main phases of your turn
Other ways to use the big mana value of split cards include Starfield of Nyx, Zur, Eternal Schemer, and Metallurgic Summonings