expect a large hit in attendence (especially when you are 0-12, etc) and especially in bleacher seats.
If it were me, I would fight to stay up, because who knows what kind of D.IV you'll demote into. If you demote into, say IV.13, or a similar one with 4+ DIII ready teams, it could be a long time until you promote. In addition, it would be boring to go 0-22!
Personally, I would just try to stay up. However if you know there is no way you can avoid relegation, and don't mind 14 weeks of boredom (and another 14 weeks of dominating a DIV-potentially), then economically it makes more sense to tank, and cut all but essential salary.