How to define 'elite athletes'?

I'm not sure I buy the premise. The most successful trainer I know doesn't train elite athletes. She wouldn't turn them away, but that is not who she markets to. She mostly does beginning to midlevel triathletes. They are the ones who need the most help, and are most likely to hurt themselves without it. She runs "boot camps" and clinics all year. She also does a lot of skills development classes. I know one thing she did to get going was to hold a series of short free intro lectures at a recreational store here that is know for those sort of things.

Just for an idea of what she gets - last Sunday I saw at least 25 or 30 people in her swim clinic at $15 a piece (she does 2 on Sundays, the second usually has more people). They ranged from need to learn in order to complete a triathlon to ones who could slowly complete a few laps. Most of these people also come for private sessions. She also does running clinics, biking clinics and transition clinics. All of them fill up. This is the group with the most disposable income, and are willing to spend some to get better. They are also the ones who understand that they need help, and will really follow what you teach them.

In that case I would say US NCAA or National level competition athletes would count. That is where most PT and kinesiology students do their internships here. A few work with professional teams, but not many due to the conflict with school and their travel schedules. I also know several who did internships with the ballet company. Around here the college teams have some of the most experienced trainers, and they are willing to work with students and then write letters for them afterwards. Over there I would think that the top level nonprofessional soccer league would count, as well as any team (track, swimming etc) with people competing at nationals or trials.

Surely elite implies a high standard of performance approaching national level. I would hesitate to call a county athletics champion, or an Accrington Stanley defender elite since neither is necessarily performing to national level, while each may be far superior to the average performer.
Payment for performance will vary from sport to sport, and cannot be used as a criterion, since some sports have a higher profile than others.