There is not one way to answer this in my opinion. There are some things to take into consideration. Are you looking for just a general distance ball or are you looking for something that gives you more performance? Like stopping power around the green or with your scoring clubs.
1) Srixon Soft Feel
2) Callaway Super Soft
3) Taylor Made Burner Soft
These are all good and affordable.
If you want a performance ball, similar to what is played on Tour, you are going to need a urethane cover. That is what really aids in the stopping power of a ball. There are two good ones to look.
More affordable Performance balls;
1) Taylor Made Project A
2) Srixon Q-Star Tour
Lastly, look for logo over runs or for left over stock from previous models. Many times when a new ball comes out there is still inventory left over from the previous generation and it will be discounted at a nice savings.