How tight of a budget?
Personally I recommend Happy Frog. I add feather meal, bat guanos, blood meals, alfalfa meal, and kelp meal and it works great. Most of the organic ammendent can be found for ~ $1/lb at stores that sell them in bulk. Check out Subcools super soil in the organics section - pretty helpful.
If you are on a tight tight budget and have very little experience just buy a bag of Miracle Grow Moisture control. Everyone will rage on you for using it but its cheap and has all the nutrients you'll need already in it - just water.