They look good enough for a site header in my terms, maybe you could play about more in Photoshop, or GIMP to see what else you can change to them, overall I would say they would most probably be worth around $5 each at the most, dependant on who would buy them.
It doesn't look like a 5 minute job, but it doesn't look expensive at all. Actually I would quote this $0.00. It is the banners that I see on those free designer request sig type of sites. heh. Sorry buddy, the designs are nice, but don't look like the right banners for the business industry where we would pay for them.