I recently did a similar Business Plan for a Engineering Business in South Africa.
This is also very similar to one I did for an Embroidery Business.
1. Machinery and Equipment Costs - You need to decide what type of work you are planning to accept.
This will determine what type of Machinery and Equipment is required.
You can then determine the cost of the Machinery and Equipment.
You can then determine a cost per unit of time per machine.
Do not make your units of time less then 15 minutes each.
2. Operating Staff Costs - The Operating Staff will have to be skilled or have to be trained in the operation of the Machinery and Equipment.
3. Infrastructure Costs - The other Costs are standard costs as pertaining to any Business Plan.
4. Then you must still determine your Ptofit percentage markup.
Check out your Competitors.
From personal experience my advice is if you don't make a minimum of 30 % nett profit, then forget it.
Good Luck !