If you can get the stickers yourself and want to spend your time and effort installing them (no big deal), and if you have no interest in supporting one of the few remaining Amiga retailers (a retailer that has a proven track record of good service and efforts to continue serving a tiny niche market filled with customers that are very hard to please) then by all means don't buy these products.
I don't mind paying AmigaKit a few dollars in return for their work to have the stickers produced and installed, but more important, I support them because they support our community with products and services that I don't want to see disappear. (Plus they are great guys and Amiga fans themselves)
I never found sticker 'installation' such a taxing job that I'd pay someone else to 'install' them as you put it.
Is this a joke?
EDIT: 100% mark up. Just as well there's so many people drinking the Kool-Aid.