We have this almost every thread, maybe we should write a short pasta for it.
Budget decks: Always look at how much money you are spending on the deck and how much of that you are spending on modern stables. Therefore, it is better to go with a single color and use a ton of basics over playing two colors and buying lands you don't want in the optimized list.
Good mono colored decks:
W - DnT, Thalia is in many creature decks and you can upgrade it with vials, eldrazis etc.
U - no good blue decks I could think of.
B - 8 rack. Drop the bridge and lilliana and it is really cheap, thoughtseize and inqusition is part of all black decks in modern.
R - Mono red burn. The only expensive card is goblin guide and you can substitute that in the beginning. Bolts are in all red decks and having
G - Mono green control is my pet favorite. It doesn't have many stables but it is the strongest of the ones I listed. Gotta love Trinisphere, land destruction and a ton of huge timmy cards.