Quick: which fertilizer is the least expensive? A $7 quick-release fertilizer or a $12 slow-release fertilizer?
The $7 fertilizer seems cheaper: after all, you paid $5 less than for the $12 fertilizer. But you have to read the label to find out which is really the bargain.
Look especially at the recommended application frequency. Quick-release fertilizers are usually designed for weekly or biweekly applications. At that rate, you may well have used up the entire box or bottle before the end of the season.
Slow release fertilizers often seem more expensive at first, but do the math: most of them are designed to be applied only once or twice a year. At that rate, it may take you a decade to go through them entirely!