The filing fee is $130 for a small entity and drawings typically cost $100 to $125 per page, so a high quality provisional patent application for a mechanical or electrical device can typically be prepared and filed for $2,500 to $3,000.y way of example, you could probably find an attorney to write a patent for a business method or computer software for quite cheap, but a cheap computer related patent would not be nearly as strong as a patent application costing $20,000 or more.