You're getting good advice. At that price point I agree it's probably Drake or ATX, but with that number of business filings I imagine Drake would be generally better if for no other reason than the depreciation module being slightly less dreadful. Maybe Proseries will give you a good deal for a new customer around that number of returns. If you get to higher end programs (Lacerte, UT, CCH) even their new client specials might be well out of your budget.
I think you need to look bigger picture. You've roughly given away your age in this thread, and I would hope that as a University professor at that stage of life, your financial needs would be more than taken care of with the main job, and the side stuff should be all gravy. After tax season is over, figure out what you earned per hour of effort in your side business, and if you had a software package that does states better, how many hours would that save? Having a side practice with this many returns means you can't have much free time, and your free time has considerable value, no?
Since you're already undercharging, a tiny fee increase shouldn't lose you many clients, if any. If you raise your rates $15 per 1040 and $25 per entity that raises enough extra fee income to move your $2,000 software budget to $4,000 with an extra grand in your pocket at the end of the day. Or, if you want to think bigger, push through an across-the-board X% increase. Taxes have gotten much more complicated and it takes much more time to do every tax return, so you need to raise rates and you probably need to get rid of some of your low-end clients, anyway.