I taught swimming for the Red Cross for 45 years. I had some pretty large "ladies" so needed a suit with a good built in bra. I couldn't afford the name brands and used five to six suits a summer, so took an old Stretch and Sew class. Wow, what a difference.
Was able to lengthen them so I wasn't pulling the back down all the time to cover the rear. Finally got pretty good at it and ended up with a business making suits for others who had fitting problems. They were very easy once I got the hang of it and because swimsuit fabric was usually 60" wide, it only took a yard or yard and a quarter. This way, I was able to buy very good fabric. We had a store here that specialized in swim fabric. My suits never cost me more than $30. I bought my bras and elastic in quanity.