Also there is a surprising number of hair coloring techniques available that are quick and cheap and won't lock your into a maintenance routine (like grown-out roots that need to be touched up every 4 to 6 weeks).
You can easily transform your hair with a few well-placed contrasting
highlights and lowlights. Ask your stylist for a consultation and explain you don't have much money to spend. Make sure you find out exactly how much it will cost.
If you want something less permanent, try clipping a few colored hair extension wefts around the bottom layer of your hairstyle.
You'll get extra length and funky hair color, which will make the most visible difference to your hair, with very little effort or money.