It looks like you have a good set of trainees, so your next priority is to get them trained.
Level 7 is probably a good fit for your budget - skimp a little on the doctor (level 1 for now) and probably level 3-4 PR for now.
You will make most of your money when these trainees get to a decent level and the trainer does help.
If you can afford it, get that trainer. Once things are going well, get the highest you can afford.