What is the best antibiotic that's cheap for a uti?

Subjective answer: The "best" antibiotic(abx) is often a matter of taste. Usually abx are prescribed without a urine culture result that helps narrow down the bacteria (out of millions) causing the UTI. Without urine sensitivity results, the most effective abx against that bacteria is unknown. Ideally, the abx will be effective against the bacteria & cause no side effects. Bactrim (sulfamethoxazole and trimethoprim) is cheap but not always effective.