If you are on a budget, i strongly suggest that you go either mono-red or mono-blue. Playing only one color gets the benefit of having mostly basinc lands as your mana base, wich reduce the cost of a deck by a great margin.The choice between the two colors also depends on wether you play 1vs1 or multiplayer.
If you play 1vs1, i would choose a mono-blue deck. Blue offers some very good generals while the red ones aren't that great or simply cost too much for what they do. Blue also offers the possibility of playing counterspells, which usually don't sell for too much money.
If you play multiplayer, i would still go for a mono-color deck but, you can pick either color and be very fine with it. In fact, red offers some good removal, while counterspells are less effective in multiplayer games.
For decklists, it would be easier if you provide some playstyle you want or any theme you would like.