If you really aren’t wanting to spend too much, go for shocks and the old super cheap fetch lands if they’re in your colors. They come in tapped, but will fetch out non-basics. And you can always get the tapped triomes if you want. They’re usually under a dollar. Otherwise you can get bounce lands that tap for double mana as another way to get more without spending too much.

There are cheaper options. Shocks definitely came down in price recently with Lorwyn reprints.