:Welcome: from PA.............
Since the windshield is what you look through to drive, I don't think you'll be going much over 4" tall and about 40" wide. Whatever money you can get should work. You can't expect to put a lot of design time into something only worth about $50. So, don't waste time on that part. If you can get $225. go for it, but don't be surprised when the next guy will do it for $45. and be totally content getting that, because he is busy in other areas and uses this for a filler job.
They take about 10 minutes to design, five minutes to cut and weed and another 5 minutes to prep and ten more minutes to clean up and collect your money.
That's an average of $100 per hour. Pretty good money doin' windshields.........