He promotes, even if he'll lose the finals.
But you need to get some stronger players (except maybe for guards, as I assume you're training those). So for starters try to find some good inside players (with high salary); if they're older, they'll be cheaper. Transfer prices are somewhat lower during the playoffs, but you can get some good deals next season as well. The money you get when promoting will help somewhat.
And when you can, build up you arena, as that's your lifeline. Experiment with the prices to find the best way to get the most out of it; as you noticed, high or max prices isn't exactly in your advantage (if at some point you'll be loosing games, you'll have an even lower attendance).
Good luck in the finals!