Look for an Advanced trainer if you really plan on training some players. You shouldn't really worry about a specialty right now either. Career Extension is meant for teams with aging players 32+ (Slows the drops a bit). Hopefully someone can chime in on Fitness as I forgot and don't want to give you wrong info there.
When you add in a specialty while looking for a low salaried trainer, prices really seem to spike, which is why I'd advise you to just look for a cheap Advanced trainer with no specialty.