If the springs are basically in good condition, and they are just a bit flat from the years of use, one possibility is to have them re-arched.
MANY years ago, I worked at a truck repair company in Amarillo Texas called Tow Brothers. (NOT a recommendation for them, Hell, I don't even know if they are still in business, this was 36 years ago) They did just about every kind of work on truck and trailer suspensions. One of the things they did was take old tired springs, disassemble them, and re-arch them to factory specs.
As I said, this isn't an endorsement for the company, but a possibility of repair if you need your springs redone. I am sure that there are many places across the U.S. that will do this for a much cheaper price than buying new.
Just a suggestion, your mileage may vary...