Here's our league's average weekly economy stats:
Player Salaries:	$ 101 087	Attendance:	$ 100 880
Staff Salaries:	$ 55 021	Merchandise:	$ 19 377
Scouting:	$ 7 857	TV Contract:	$ 67 151
Total:	$ 163 965	Total:	$ 187 408
League Average Net Income: $ 23 443
I spent most of the season at ~80K total player salary, and currently I'm leading my conference. But of course you know that salary is not a great metric for determining player performance. But just about all of my players were 7-10K weekly salary. And they were fine. And three of those guys were my main trainees. 
If you're set to promote, I'd suggest getting ready to put a good chunk of that cash reserve into your arena. Then, after the playoff eligibility deadline, I would look to pick up some cheap veterans, especially for depth. 
Note you'll also receive a 200K promotion bonus when the season turns over. I put my entire bonus into my arena, and and glad I did.
I'll second what Sharkboy said.
Our league averages in IV.41:
League Averages from Last Week
Expenses 	Revenue
Player Salaries: 	$ 118 203 	Attendance: 	$ 120 426
Staff Salaries: 	$ 44 056 	Merchandise: 	$ 20 230
Scouting: 	$ 11 250 	TV Contract: 	$ 68 018
Total: 	$ 173 509 	Total: 	$ 208 674
League Average Net Income: $ 35 165
The part about finding quality veterans after the playoff deadline is advice that is absolutely outstanding. The demand should be much lower at that point and hopefully you will find players that will fit well. I'd encourage trying to get well-rounded players at good salary points rather than monster salary guys with major holes in their game, too. There's a lot of bang for your bucks that way.
You also definitely want to improve the arena, since that's the foundation of your economy.