I always use this water based stain from Clou.
It's cheap (like 5 euro per sachet)
And very easy to use. Just dilute it in lukewarm water. (after it has cooled down you can keep it in a bottle forever)
You can blend colors if you want, by putting the pigment powder together. But that is always a bit of a gamble.
Not that you'd need to blend them really, because they have quite a color range to chose from. Here are some examples: