In a season I think you can get easily at least 1 million no matter the league (yes, no matter the league). Here's how.
1. Get 2 trainees, 1 position train them the whole season. Let it be 18 year olds. At the end of the season you can sell each of them for 300-400 k. Sometimes even more. I sold my trainee at early 19 for 760 k. I'm sure other managers have even better success stories.
2. Invest in your arena. Every penny you get, buy some seats. Correct the prices when certain seat type is selling over 90%. Construction completes and you have some money? Invest again. The whole season. At the end of the season your attendance will increase so much you'll increase ticket prices considerably. :)
3. Invest in scouting. 40 k. Yes, maximum. Especially if you're going to finish bottom of the league. If you get 1 or 2 draftees that are either with good starting skills or with high potential, you can sell them too and get some serious amounts of money. Sometimes an 18 year old gets sold for 3 million just because of his potential. So I think draft is really important.
Just make sure your weekly income is always positive. So next season you start hopefully with loads of cash. :) Let's not forget you get some money if you promote too. So if all goes as planned, say 2x500k for trainees, at least 500 for draftee, 300k for promoting and you have your arena built. This is pretty real expectation.