Really, there couldn't be anything much easier to make yourself. There are lots of options, of course, but I'm talking about the basic tomato/onion/chilli variety.
Actually that's almost the whole recipe (LOL).
I'd suggest about
3 - cups of chopped tomatoes -- keep the juice and seeds, use the whole fruit.
1 medium to large onion chopped (depending on your preference)
2-3 chillis, roasted, peeled, chopped (see below)
1 Bunch of cilantro coarsely chopped
juice of lime and juice of lemon
salt and pepper to taste
*Chillis (or peppers as they're called) are your wildcard in a salsa. How much heat do you want in your salsa. Mild to Inferno is possible. I'd suggest two Anaheim and one Jalapeno to start. No matter which chillis you use, roast them over your stove burner til the skin blisters and chars. Place it in a bag (paper or plastic) for 20 - 30 minutes for the skins to loosen. Now, iIf you like mild salsa, then peel and remove the seds and ribs from inside. That's where the heat of the pepper is "stored" in the fruit, so you can control heat by leaving some or all of that material. For a real thrill, try a habanero.
Let the mixture "meld" in the fridge for at least 30 minutes. Lasts for two - three days in the fridge.
Ole