3 lvl 1s
Hello.
Being that you only have three PCs, and they're all level 1, your options are going to be a bit limited. Encounter design gets a lot better with more PCs, and when they get a few levels. For an "average" encounter, you have 300 points to play with. The "more challenging" (+1 level) encounter gives us a 400 point pool. Let's go with one of those. The stereotypical lvl 1 encounter would be a kobold ambush, but if you want this to occur while they're camping at night, undead or bandits is another option.
Kobolds
As the PCs walk down the road, kobolds hide in the bushes. When the PCs walk over square X, a kobold slinger triggers a Rockslide trap set to go off at that location. The slinger tries to Gluepot PCs in the rockslide. When the dust settles, the minions and skirmisher run amok while the slinger continues to fire at range with regular bullets.
Rockslide 100xp
4x Kobold Minion 100xp
Kobold Skirmisher 100xp
Kobold Slinger 100xp
Undead
Just about as simple as it gets. Various undead have picked up the scent of the living and simply march into the camp looking for a meal. Braaains. The PCs will have a tough time with this encounter if they don't take out the Deathlock Wight ASAP.
Deathlock Wight 175xp
Skeleton 150xp
2x Zombie Rotter 76xp
Bandits
Again fairly simple, but the bandits at least try to use stealth to surprise the presumably lone PC on watch. The Bandits do the sneaking while the Rabble lie in wait nearby. Should be a pretty straitforward fight once the PCs get over the initial surprise and chaos.
2x Human Bandit 250xp
5x Human Rabble 155xp
Even on a 300-400 point budget, you can mix and match in a lot of thematic ways to come up with some workable encounters. And like I said, it only gets better once you have some leeway to work with once they get a few levels.
Later!
Gruns