There just isn't anything generic to go off of. We have done jobs ranging from $150/acre to $13,000 per acre. There is no shortcut. Good judgement comes from experience. Experience comes from bad judgement.
Do not expect to buy a machine and be able to find enough work to pay for it. It takes time to build the business and your reputation. There are some mulching contractors out there that do terrible work. Sometimes this leaves a bad taste in a customer or organizations mouth, and they just assume that that's what all mulching looks like. This makes it hard to get a foot in the door, but easy for repeat business if you do a good job.
Consider it a very expensive hobby for the first few years. If you have the financial backing to support that, do quality work, and sometimes takes a loss to make the customer happy, you can build a successful business.
If not, you could go to work for a reputable mulching contractor in your area. Honestly, you will probably make more money, and you can decide if it's something you like without going in debt for $125K.