Plan prices

[2020]

I purchased Chief several months ago, because I love drafting, drawing plans, elevations, etc. Recently, a couple of home builders got their hands on some of my work, and asked me to give them a price on about 30 different models, ranging from 1,000 to 3,000 square feet. They are looking for dimensioned floor plans, an elevation page, a sales page, a foundation plan, and possibly a utility plan, all in 8th inch scale. This is no problem for me to take care of, but I don't know what to charge! Can someone clue me in on the going rates? Is there a general price per square foot, or do you charge by how rich the guy is??? Please help!! Thanks in advance!