As Shane has said
Take into account how long it is going to take you to do the job including gaining access to the inside of the window-moving stock, racks etc- and cleaning the window prior to fitting the graphics. See if you can get the client the clear the area before you arrive.
If it is a new shop you may have to clean white wash off the widows which all takes time.
Don’t forget the time it takes to get to and from the job
Another way of pricing is to price per letter
Search on google for “vinyl letter price” or “price per vinyl letter” something like that and it will bring up companies who supply letters on the web.
You will find that a lot of these companies charge about the same for similar size letter which means they have done some research into the subject.
You can use these prices as a starting point for working out your own prices
Use their prices per letter add your labour cost and travelling time and see what it brings up
Post the results on here and people will soon let you know if your prices are way off
good luck with your new business and get this bit of the job right as soon as possible
Once you have worked out a system for pricing it will make your life easier and your prices consistant.
Hope this helps
paul r