"He's asking me if he can try swim team. He absolutely loves to swim, so maybe this will be for him. It's so expensive!"
You might want to figure out what DS loves about swimming and see if there is anyway for him to "sample" before you make a commitment. My DD10 loved to swim and thought that swim team sounded great. Our pool ran a clinic before the season to get the kids back in shape. They also allowed kids to participate in an inter-squad meet before they made a commitment -- as the coach put it, no one wants a kid who doesn't want to be there. My daughter did the clinic and hated it. She hated swimming laps with other people, didn't like people telling her how to swim faster, and found the noise of the indoor pool where the clinic took place overwhelming. She learned that she loved the feel of the water and the peacefulness of swimming laps at her own pace. Love of swimming does not = love of swim team.