With respect,
It was mentioned that perhaps you ned to upgrade your arena.
You are just a few seats away from 5k seating capacity.
Keep the lvl 4 trainer and invest in your house. That move will pay you back 100 times over alone.
I personally did this for about 6 seasons and dropped no less than 2k seats per season. After investing in the only real source of income for you, you may wish to consider a lvl 6 trainer.
Just my 2 cents but many GMs put the cart in front of the horse.