Where should i buy my suits

For my occupation i am required to wear three piece/ vested suits. Two piece would only be worn on a casual friday kind of thing which we never have. My question is where should i buy my suits because im sick of having them all custom made. Its expensive and im 18 and i keep growing out of them. I prefer to wear my suits in pinstripe or window pane pattern. Any suggestions from the $450 to $700 range for apparel stores i can shop at?