so for jobs like lets say someone wants only 5 6"x1" decals, if your charging $12/psf it should be $12 since it fits within that square foot?
6"x1" is rather small so I always try to upsell them on adding some type of image to the "Loving Memory" to make it even more personal. 99% of the time customers like the idea. If they still want it that size I tell them my standard charge of $1.00 an inch for the longest side and that 6"x1" can have the image included for the same price as long as it stays 6 inches on the longest side. I also let them know that any custom work must be charged a minimum of $10.00 otherwise not worth my time to create it. Then if they want 5 like you said, I will give them a quantity discount since the first one is the one you had to spend time on the layout, the rest is just cutting, weeding, and taping. So 5 decals at 6inch long is $30 and since they buy in quantity, knock off a couple of bucks if you wish. Since it is a memorial, the customer usually likes to have it "represent" that person. Upselling them to add an image not only adds a personal touch, it allows you to get a bit more for your time invested.
By upselling them on adding an image, you can make more than $12.00 a square foot. You can make $25.00 sf and give your customers something a bit more than text for that memorial of their loved one.
As far as installing, I don't charge if it is something that only takes a few minutes. As long as you dont have to scrape mud off the vehicle or travel to do the install, why charge? If you feel like you need to charge, then just charge a buck or two per decal, nothing major.
Matt
P.S. I sold 3 decals (5"x4") recently for $15 and installed them free of charge. End result = I got $30 a sf if you lay it out right. 3 decals 5x4 would take 5x12 of vinyl, half a square foot, so half a sf for $15 would come out to $30 for a square. I got paid a decent price for smaller weeding and the customer is very pleased with results and price.