Like any craftsman, a taxidermist is paid for finished products. The average price of a deer mount is $300-$400, but you can charge more the better you get. A full-time taxidermist should be able to get by on less than $20k a year. The real reward comes from competitions, and those are getting really popular.
Each mount takes months, sometimes years to complete, so you have to plan and budget accordingly.
The economics and record-keeping of taxidermy are…boring. Get an accountant or work for a large taxidermy place. Always keep those receipts. The IRS might ask if your nose brushes are for personal use.
Don't forget the cost of supplies, travel to conventions, tuition, and membership fees.