Time for some back of the envelope math. What do you think the realistic selling price of your product or service is? Top of your head based on everything you know about the industry. Now how much do you think it will cost you to deliver this product or service? Think concerning the actual variable cost - no overhead like insurance, accounting, taxes, legal, etc. Take selling price minus your cost and you have a guess at a gross profit per unit sold. Now take Your Number and add a guess for overhead such as advertising, office space, etc. $10-20K is suitable for most small businesses. This value is your total cost. Now divide your total cost by your gross profit. This total is how many units you will need to sell just to break even. Divide the unit sales by the number of days you wish to work, and this is how many units you will need to sell each day to break even. Is it possible?
The first few times you do this, it will be probably not possible to produce the volume you need to break even. The point is to make a few educated guesses and quickly slice down through your ideas to find one that works on the back of a napkin.
Selling Price Per Unit - Variable Cost Per Unit = Gross Margin Per Unit
Your Number + Overhead = Fixed Cost
Fixed Cost / Gross Margin Per Unit = Unit Sales to Break Even
Unit Sales to Break Even / No. of Desired Working Days = Sales Per Day to Break Even