I got a spoiler since I cracked mine and heres what I can pass on about blending and paint information. First and formost, call around. Second, I can not recomend bondo for that size of hole, you are better off welding and grinding the same day you plan on taking the car to the shop, or the night before. When you weld the hole shut, grind it down then using a putty knife apply the bondo over the weld and let it set up. Do your sanding with a block (you can use a block of wood and sandpaper) at about 320 grit and then I went from there to 600 to 800 to 1200. You just want to get rid of all the high spots. It's better to start high and work low untill you get rid of almost all the bondo than to find a big low spot in the bondo/weld. After you have it all bondo'd up take it to the shop, the area you had to sand they will cover and blend and clear coat. For my spoiler it took them a total of 2-to-4oz of paint (didn't matter that it was metalic they will only change price if its chameleon) and about 6oz of clear. The total cost to have them paint the spoiler and blended for me was $150. The bodyshop will only charge for what they use, not per pint or quart or whatever.
A note on blending, depending on how faded the paint is will determine the amount of blending. I cant tell from your picture but if it is the KM metallic blue like my car it wouldnt cost anything more than regular paint. You're lookin at about maybe a $75-100 job, or at the worst $150.
